In a warning shot to outside conservative groups, the National Republican Senatorial Committee this week informed a prominent Republican advertising firm that it would not receive any contracts with the campaign committee because of its work with a group that targets incumbent Senate Republicans.

Even more striking, a senior official at the committee called individual Republican Senate campaigns and other party organizations this week and urged them not to hire the firm, Jamestown Associates, in an effort to punish them for working for the Senate Conservatives Fund, a group founded by Jim DeMint, then a South Carolina senator, that is trying to unseat Senator Mitch McConnell of Kentucky, the Republican leader, and some other incumbents up for re-election next year whom it finds insufficiently conservative.

“We’re not going to do business with people who profit off of attacking Republicans,” said Brad Dayspring, a spokesman for the committee. “Purity for profit is a disease that threatens the Republican Party.”

The committee has conveyed the same message, privately, to 2014 Senate candidates, the Republican National Committee, the National Republican Congressional Committee (the senatorial committee’s House counterpart), the Republican Governors Association and Mike DuHaime, the chief strategist for Gov. Chris Christie of New Jersey, for whom Jamestown also does work.

Jamestown declined to respond to the attempt to curtail their business, deferring to the Senate Conservatives Fund, which criticized Mr. McConnell.

“This is happening because Mitch McConnell is having a complete meltdown,” said Matt Hoskins, executive director of the conservative group. “He can’t defend his record so he’s threatening and attacking everyone who disagrees with him. He’s so rattled, he has decided to declare war on the entire conservative movement, which represents the very people he needs to win re-election. This isn’t the behavior of a confident person. It’s the irrational reaction of a power-hungry bully who isn’t getting his way.”

Some of Jamestown’s conservative clients also moved to defend the firm.

“When some in Washington stepped away from our campaign, Jamestown stood with us and fought,” said Representative Mark Sanford, Republican of South Carolina. “I think their team is a good one and what a few in D.C. decide isn’t going to change that.”

The National Republican Senatorial Committee’s power play is part of a larger effort among establishment Republicans after the recent government shutdown to seize control of the party from insurgent forces who want to push Republicans toward a more hard-line posture and aggressive brand of conservatism. The attempt to effectively blacklist the consulting firm illustrates the extent of the tensions between the establishment and the hard-liners.

Mr. McConnell’s allies in Washington’s lobbying community have been furious for weeks that Jamestown, which also does work for groups like the Republican Jewish Coalition, was on retainer with the Senate Conservatives Fund.

One prominent Republican lobbyist even printed out the records of a Louisville television station detailing the run times of every ad devised by Jamestown for the conservative group’s campaign against Mr. McConnell and gave it to a reporter.

“These are not the kind of people we would ever do business with,” said Scott Reed, senior political strategist for the U.S. Chamber of Commerce.

In the wake of the shutdown, Mr. McConnell and his top aides are also becoming more outspoken about wanting to effectively destroy the Senate Conservatives Fund. The senator has told donors that he and other party leaders will take a much more aggressive approach in confronting such conservative groups.

And on Friday, one of Mr. McConnell’s closest aides offered a vivid metaphor about the leader’s determination.

“S.C.F. has been wandering around the country destroying the Republican Party like a drunk who tears up every bar they walk into,” said Josh Holmes, Mr. McConnell’s chief of staff, now detailed to the National Republican Senatorial Committee through the election. “The difference this cycle is that they strolled into Mitch McConnell’s bar and he doesn’t throw you out, he locks the door.”