WASHINGTON—Conservatives panned the House Republican proposal released Monday to avoid the so-called fiscal cliff, yet again giving House Speaker and lead negotiator John Boehner little room to maneuver as he works toward a deal with the White House.

The proposal includes extending current tax rates for all income levels and raising revenue by closing loopholes in the tax code.

"Rarely in modern American politics have more counterproductive, more foolish words been set to paper," wrote researchers at the Heritage Foundation in response to part of the letter sent to the White House from seven House leaders that outlined the Republican plan. The Heritage analysis, co-written by Alison Acosta Fraser and J.D. Foster, went on to say: "[T]he Republican counteroffer, to the extent it can be interpreted from the hazy details now available, is a dud. It is utterly unacceptable. It is bad policy, bad economics, and, if we may say so, highly questionable as a negotiating tactic."

Heritage's response echoed the sentiment of many conservatives in Washington who are urging House Republicans to avoid cutting a deal with the president if it means raising taxes.

In an open letter signed by more than 100 prominent conservative activists and organized by the advocacy group Let Freedom Ring, House Republicans were warned that they would not receive support in the future if they "cave" during negotiations.

"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," the letter read. It was signed by Republican activists like Richard Viguerie, Leadership Institute founder Morton Blackwell, Eagle Forum founder Phyllis Schlafly, Media Research Center President Brent Bozell and Republican donor Foster Friess.

"And if Republicans cave in now, when it really counts," the letter continued, "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."

Story continues

In the Senate on Tuesday, South Carolina Republican Sen. Jim DeMint, one of the tea party's staunchest allies in the upper chamber, accused House Republicans of promoting a plan that would "destroy American jobs."

DeMint's remarks this week, however, seemed to be somewhat of a departure from his characterization of a possible deal before the election, when he said Republicans who don't want to see the automatic defense spending reductions set to automatically trigger next year go into effect "might as well cut a deal" that includes tax increases.

"You can't get a deal with Obama without raising taxes on the producing class of folks," DeMint said in September, according to a report by Bloomberg News. "We might as well cut a deal. If Republicans want to maintain the defense, we're going to have to give tax increases to Obama."

In a statement to Yahoo News, DeMint's spokesman moved to clarify the remarks, saying that he had "simply stated the obvious" and would never support a plan with more taxes.

"Before the election, he simply stated the obvious, that Obama would try to use a lame-duck session to rush through tax hikes that will hurt the economy," DeMint spokesman Wesley Denton said. "His point then was that if Republican leadership wasn't going to stand strong against tax hikes in the lame-duck, they might as well be honest with voters before the election. Sadly, his predictions have proven correct and his long opposition to tax hikes that destroy jobs hasn't changed."

The conservative backlash, of course, could amount to mere noise as Boehner continues his negotiations with the president in search of a deal. The speaker and his allies in the House have spent two years navigating the thorn-riddled path between his party's conservative base and Obama's demands.