"The American people don’t want this trillion dollar political payoff that will just line the pockets of non-governmental organizations who supported [President] Obama in the election,” said Scott Wheeler, the executive director of The National Republican Trust PAC, an organization that calls for less government spending and lower taxes.
“Republican senators are on notice," Wheeler said. "If they support the stimulus package, we will make sure every voter in their state knows how they tried to further bankrupt voters in an already bad economy.”
In a Senate vote Tuesday, only three Republicans backed the $838 billion measure — Sens. Olympia Snowe and Susan Collins of Maine, and Pennsylvania Sen. Arlen Specter.
All three senators were involved in cutting spending proposals from the plan, and have said they may not vote for the final version bill if more spending projects are added to it.
The group's pledge appears most threatening to Specter, the only GOP supporter of the bill who faces reelection in 2010. A longtime moderate, Specter has faced tough primary challengers in the past, including Club for Growth President Pat Toomey's 2004 primary challenge.
"[Sen. Specter] crossed the line one too many times," Wheeler told CNN. "We're now going to get involved in finding a conservative alternative."
Toomey has said he is not interested in running again, and another credible challenger has yet to emerge in the race. Still, Specter’s decision to serve as one of only three GOP enablers to the stimulus bill has irked many Republicans in his home state and may have virtually guaranteed a primary fight.
Speaking to CNN Tuesday, Specter said his vote has resulted in a flood of negative phone calls to his office and predicted it would lead to a tough primary battle.
"I have no doubts about the political disadvantage," he said. "[I'm] losing a lot of political skin about this and I've got a primary battle coming up in about a year…it means I'll have to raise a lot more money."
Sens. Collins and Snowe did not return CNN's request for comment. Collins solidly won reelection last November and Snowe's seat is not up until 2012.
The PAC's pledge comes the same day another conservative group launched a series of robo-calls in Pennsylvania and Maine, urging constituents to call their Republican senators and demand they stop supporting President Obama’s stimulus package.
Delaware-based ‘Let Freedom Ring’ began running 100,000 robocalls Tuesday in Pennsylvania and 50,000 more calls in Maine, according to Colin Hanna, the group’s president.
“Would you be willing to contact your senator Arlen Specter today and tell him to vote no on the Obama tax and spend plan?” the Pennsylvania call asks, before providing a phone call for Specter’s Washington office.
– CNN's Peter Hamby, Dana Bash, and Evan Glass contributed to this report