Driven by growing concerns that House GOP leaders will give in to raising tax rates, grassroots conservatives are ramping up pressure on Republicans to block any deal on the fiscal cliff.

More than 100 conservative leaders — including Santorum megadonor Foster Friess, RedState editor Erick Erickson, Phyllis Schlafly, longtime GOP activist Morton Blackwell, and others — banded together Wednesday to send an open letter warning Republican members of Congress against voting for any compromise on the fiscal cliff.

"The thrust of the letter is to remind Republicans in the Congress that this is a time of testing," said Morton Blackwell, a veteran Republican Party activist who hosts the exclusive Weyrich Lunch conservative strategy sessions. "The pressure is on to cave into the demands of president Obama and the left....They need to understand or be reminded that to cave in would be very bad and very much damage the credibility of the GOP

The letter, Blackwell told Business Insider, is "meant to help stiffen backbones and to let people know that there would be consequences to their political careers."

The warning underscores the significant obstacles Republican Speaker John Boehner must overcome to reach a deal with the White House on the fiscal cliff. Facing a divided caucus, it is unclear if the GOP leadership can drown out its vocal far-right faction and cobble together enough votes to pass a bill that gives in to Democrats' demands to raise tax rates on the top 2 percent of earners.

It also highlights the potential threat to Boehner's speakership should he reach a deal with Democrats. In the letter, conservatives warn that they are ready to "systematically" replace the Republican congressional leadership.

"I hope it doesn't come to that but there are failings — there are bad signs," Blackwell said, adding that conservatives were aggravated that Republican House leaders have agreed to additional revenue as part of the deficit deal, and by Boehner's decision to "purge" four conservative congressmen from key House committees.

Read the full letter and list of signatures below:

December 12, 2012

An Open Letter to U.S. House and Senate Republicans

Dear Republican U.S. Representatives and Senators:

You are entering into a period of testing.

In the House, the nation elected in 2012 one of the largest Republican majorities in the past 100 years. You have a mandate to fight for conservative principles that is arguably much broader than the one that narrowly reelected President Barack Obama claims to have for his leftist agenda.

Of course, House Republicans alone cannot pass a law, but united you can stop any bill which violates the principles you publicly committed to support.

In the Senate, you have more than enough Republicans to prevent the passage of anything truly harmful to our country.

Nevertheless, you are already being pressured to abandon the principles voters elected you to uphold.

The major news media, Democrat politicians, liberal interest groups, and even some weak-kneed Republicans are demanding that you not use the powers given to you by the electorate to stop the power-grab agendas of President Obama, Senate Majority Leader Harry Reid, and House Minority Leader Nancy Pelosi.

The Democrat leadership does want to "fundamentally change" America.

They want to increase federal power, federal spending, federal taxes, federal deficits, and federal debt. They want to give more advantages to their liberal allies and put more federal money into the pockets of their political cronies.

They want to undermine further traditional values and to surrender more of our national sovereignty to international bodies.

They want to weaken our country militarily and move America more rapidly in the direction of European socialism.

Their entire leftist agenda opposes the principles on which you ran and the principles of the millions of people who elected Republicans to Congress.

And now we count on you to stop them. Nobody else can stop them but you. You have the power, if you will use it.

The whole leftist apparatus is gearing up to panic you and to force you to cave in. Don't do it.

All of them, the liberal Democrats, the labor unions, the leftist ideologues in the so-called "progressive" movement, and their allies in the print, broadcast, and online media will try to convince you that your political careers will be over if you don't cave in.

Let us remind you that these same people have always tried to defeat you -- yet you won election.

Whether your resistance to their current power grabs collapses or not, they will work just as hard to defeat you next time. But if you are seen to cave in now, next time they will be stronger.

And if Republicans cave in now, when it really counts, next time you will be weaker, because your conservative base will be outraged. Many who worked hard to elect you in the past will never lift a finger for you again.

There are two ways President Obama, Nancy Pelosi, and Harry Reid could get what they want out of the Congress now.

First, just enough Republicans could vote with the Democrats and against most other Republicans to pass what Obama, Pelosi, and Reid want passed.

Second, the Republican leadership could negotiate a "deal" with the Democrats and take most Republican Representatives and Senators with them.

Either of those two courses would be a disaster for conservative principles because they would result in permanent advances for the "fundamental changes" the left wants to impose on our country.

Let us also remind you that a great many potent conservative organizations and millions of conservative and liberty-loving voters do not believe in the divine right of incumbents to be re-nominated. Conservatives know how to recruit and support candidates.

In recent election cycles the left has virtually eliminated "moderate" Democrats from the Congress. And you have no conservative Democrat colleagues at all.

At the same time, those election cycles have resulted in the nomination and election of fewer and fewer Republicans who play footsie with liberal Democrats.

In the Republican Party, conservatives dominate the primaries more and more, a process almost certain to continue.

Not only do you now have one of the biggest House Republican majorities in the past century, in the Senate, you have 45 Republicans, more than enough to stop many bad decisions there.

Suppose just enough Republicans cross the aisle to provide Democrats a majority in vitally important legislative battles now upon us. They will find themselves, come election time, the targets of both liberal Democrats and conservative Republicans, which isn't likely to be healthy for their political careers.

Suppose, on the other hand, that the congressional Republican leadership negotiates a "deal," a "compromise," with Obama, Pelosi, and Reid.

The historic record of such deals shows that the Democrats usually clean the Republicans' clocks.

You will remember that, with all good will, President Reagan and then the first President Bush made deals to support some tax increases in return for Democrat promises to cut spending even more. In both cases, the new taxes were quite real, but far from cuts in spending, spending increases followed.

Right now it is generally but incorrectly believed that Republicans aren't able to negotiate from a position of strength.

Of course, this time every element of the left will be in full-throated roar, yelling that the country will collapse if Republicans don't give in to their demands.

There is some danger that the congressional Republican leaders will decide to accept whatever deals they can get, which might mean that Democrats get real gains and Republicans again get empty promises. Or Democrats would get permanent changes and Republicans would get changes easily reversed by a future Congress.

If such deals are made, conservative organizations and conservative and liberty-loving voters would see that the current leadership is not an acceptable alternative to the left. Conservatives would then likely repeat what they did in the 1970s, when they systematically and successfully undertook a multi-year effort to replace Republican congressional leadership.

With President Obama in office for another four years and his leftist appointees working tirelessly to implement the left's agenda, there is a virtual certainty that the economy will not have a significant recovery. More likely the country will suffer a continuation of Obama's permanent recession.

Yes, this is a time of testing for you.

If Republicans provide a consistent, conservative alternative, the time will come, probably sooner than later, when most Americans will become fed up with the left's failed agenda and be ready for a change to "throw the bums out" and restore limited, Constitutional government.

So it's in the interest of the country and in your personal interest for you to use the power you unquestionably have now to stand firm and not surrender your conservative principles, no matter how loud the clamor of people whose central interest is to advance the left's agenda.

Sincerely,

(Affiliations for identification only)

Morton Blackwell, Chairman, The Weyrich Lunch

Colin Hanna, President, Let Freedom Ring

Ed Meese, Conservative Action Project

Jim Martin, Chairman, 60 Plus Association

Phyllis Schlafly, President, Eagle Forum

T. Kenneth Cribb, Jr., National Conservative Campaign Fund

Brent Bozell, President, ForAmerica

Tom McClusky, Sr. Vice President, Family Research Council Action

Hon. James S. Gilmore, III, President, Free Congress Action

Gary Bauer, President, American Values

Michael Farris, Chairman, Home School Legal Defense Association

Preston Noell, III, President, Tradition, Family, Property, Inc.

Penny Nance, CEO and President, Concerned Women for America

Shari Rendall, Director of Legislation & Public Policy, Concerned Women for America

Richard Viguerie, Chairman, ConservativeHQ.com

Al Cardenas, Chairman, American Conservative Union

Erick Erickson, Editor, RedState

Ken Blackwell, Chairman, Ohio Faith and Freedom Coalition

Foster Friess (WY)

Tim LeFever, Chairman of the Board, Capitol Resource Institute

David N. Bossie, President, Citizens United

Frank Cannon, President, American Principles Project

Susan Carleson, President, American Civil Rights Union, President, Carleson Center for Public Policy

Lori Roman, Regular Folks United/Rosies Project

Amy Ridenour, President, National Center for Public Policy Research

Mark Fitzgibbons, American Target Advertising

Seton Motely, President, Less Government

Ginni Thomas, Liberty Consulting

Phil Kerpen, President, American Commitment

Cindy Chafian, President, The Mommy Lobby

Bob Reccord, Executive Director, Council for National Policy

Jim Backlin, Christian Coalition of America

Amb. Hank Cooper, Former SDI Director

Rick Scarborough, President, Vision America

Reverend Lou Sheldon, Founder and Chairman, Traditional Values Coalition

Andrea Lafferty, President, Traditional Values Coalition

Nina May, Chairman, Renaissance Women, Renaissance Foundation

Joseph Farah, Editor and Chief Executive Officer, WND.com and WNB Books

Dr. Jim Garlow, Chairman, Renewing American Leadership Action

Janice Shaw Crouse, Ph.D, Beverly LaHaye Institute

Mathew Staver, Chairman, Liberty Counsel

Deryl Edwards, President, Liberty Counsel Action

Mandi Campbell, Legal Director, Liberty Center for Law and Policy

Rod D. Martin, Chairman, The Vanguard Project

Kay R. Daly, President, Coalition for a Fair Judiciary

Tim Echols, Chairman, Georgia Public Service Commission

Jeff Gayner, Chairman, Americans for Sovereignty

Ron Pearson, Council for America

Elaine Donnelly, President, Center for Military Readiness

Michael Centanni, Chairman, Freedom’s Defense Fund

Ted Baehr, Movieguide

Kristan Hawkins, President, Students for Life of America

Larry Cirignano, Faithful Catholic Citizens

Stu Epperson, Salem Communications Corporation

Dr. Day Gardner, President, National Black Pro-Life Union

Kevin L. Kearns, US Business and Industry Council

Rich Bott, President, Bott Radio Network

Dick Bott, Chairman, Bott Radio Network

Gary Aldrich, President, Patrick Henry Center for Individual Liberty, Chairman of the Board, Council National Policy

Gary A. Marx, Executive Director, Faith & Freedom Coalition

Tim Macy, Vice Chairman, Gun Owners of America

Bradley Mattes, Executive Director, Life Issues Institute

Floyd Brown, President, Western Center for Journalism

Cullen Davis, Ken W. Davis Foundation

Ken Timmerman (MD-08), Republican Candidate for Congress 2012

Richard W.C. Falknor, Chairman, Maryland Center-Right Coalition

John Kwapisz, Washington Liaison, American Council for Immigration Reform

Wes Vernon, RenewAmerica.com

Dianne Edmondson, Executive Director, Republican National Coalition for Life

Keith Mason, President, Personhood USA (CO)

Richard Ford, Heritage Alliance

Jason Jones, President, Movie to Movement

Melissa Ortiz, Ms. Wheelchair NY 2005, Founder & Principal, Able Americans

Jim Simpson, Freelance Investigative Journalist

Terri L. Burl, Forest County Republican Party Media, Social Media Director, Common Sense Campaign (AL)

Liz Reiten, Chair of the Florence County Republican Party,

Christ Martinson, Secretary, Wolf River Area Patriots (WI)

Penna Dexter, Co-Host, Point of View Radio Show

Todd Dexter, President, Todd Dexter & Associates

Donald Gaines, Founder & Local Coordinator, Covington County Tea Party Patriots (AL)

Mike Diggs, Tea Party Patriots of North Alabama

Seth Cowan, President, Wolf Area Patriots (WI)

Karen Schroeder, President (WI), Advocates for Academic Freedom, TeaPartyPerpective.com, Wisconsin

Troy Newman, President, Pro-Life Nation

Somers H. White, President, Somers White Co., Inc.

Roy Stringfellow, M.D., Advanced Gynecology, LLC

Penna Dexter, Radio Host

Bob Ellis, American Clarion (SD)

Judson Phillips, Founder, Tea Party Nation

Kelly G. Berry, President, The Madison Institute Association

Mark D. West, President, Chattanooga Tea Party (TN)

Dave Kramer, Dubuque County Tea Party (IA)

Cathie Adams, President, Texas Eagle Forum

Tammy Kobza, Iowa State Director, Iowa Eagle Forum

Jim Treat, Chairman, BV Tea Party Patriots

Becky Gerritson, President, Wetumpka TEA Party of Alabama

Robert K. Fischer, President, Fischer Furniture, Inc.

Tina J. Benkiser, Attorney & Counselor at Law, Fr. Republican Party of Texas Chairman

Kirk Elliott, Ph.D., TodaysAmerica.com

Dee Park, Chair, Moore TEA Citizens (NC)

Suzanne (Zan) Green, Founder, Rainy Day Patriots

J. Keet Lewis, Texans for Conservative Principles PAC

Joshua Charles, Rediscovery Project, William Jessup University

David Y. Denholm, President, Public Service Research Council

Harold Sorensen, Americans Must Investigate Public Servants

Lisa Becker, President, Liber8Congress

Jodi McDade, Member Alabama Republican Party Executive Committee

Lee A. Beaman, Entrepreneur, Nashville, Tennessee

Joseph Schwartz, North Woods Patriots (WI)

Kim Simac, President, North Woods Patriots (WI)

Kirsten Lombard, Organizer, The Wisconsin 9/12 Project

Seth Morgan, Former State Representative (OH),, Board Member of Citizens for Community Values,, Conservative Coalition Leader

Sidney E. Johnson, M.D., Member Wood County Republican Party, Member Central Wisconsin Tea Party

Ron Hei, Common Sense Tea Party Patriots of Covington County, AL

David Cook, DCC, Inc.

Tricia Erickson, President of Angel Pictures & Publicity and Crisis Management Incorporated

Dale Beach, Montgomery Tea Party Patriots (AL)

Sharon Glass, President, Santa Rosa TEA Party

Jerry A. Johnson, President, Criswell College

Bobbie Patray, President, Tennessee Eagle Forum

Daniel J. Stafford, Representative, Walton County Patriots, Florida

Ken Settle (WI), Northwoods Patriots of Eagle River

Dr. Terry B. Batton, Founder and President, Barbour County, Alabama Tax Enough Already Party

Kirk Hays, North American Jet

Tearlach F. Sinclair, Menominee County ACE, Americans for Constitutional Enforcement

Jeffery Horn, Prairie Patriots (WI)

Sidney E. Johnson, M.D., Member, Wood County Republican Party, Member, Central Wisconsin Tea Party

Becky Hall, President, Northern Liberty Alliance (Northern Minnesota/Wisconsin)

Donna Hearne

Peggy Dau

Peter Weyrich (VA)

Mr. Jeffrey L. Kirschmann

Dan Curan

Jim Coursolle (WI)

Ellen Grigsby

Dr. William Greene, President, RightMarch.com

Dr. Shelli Jones Manuel, CEO: Harvest Projects International Inc., CEO: Resurrect America Show, EXECUTIVE DIRECTOR: Sing It America

Bud LaCoy, Americans for Constitutional Enforcement, Marinette County

*This post has been updated from an earlier version posted at 1:34 p.m.