(CNN) - Several Republican senators said Wednesday they were surprised and angered after a news report revealed that their GOP colleague, Sen. Ted Cruz of Texas, made a recent fundraising appeal for a tea party group that is trying to defeat GOP incumbents it doesn't believe are conservative enough.
The senators said Cruz's efforts appeared to violate his own pledge to no longer target sitting Republican senators in favor of tea party-backed candidates in the hard-fought 2014 campaign in which Republicans believe they have a chance to win back control of the Senate.
In addition, the fundraising appears at odds with Cruz's position as vice chairman of the National Republican Senatorial Committee, the organization that works to elect and re-elect Republicans to the Senate.
"I am stunned that Senator Cruz is involved in this fundraising effort for a group that has targeted his colleagues in the Republican caucus," Sen. Susan Collins, a Maine Republican, told CNN.
"I'm particularly surprised because I thought he had agreed to no longer engage in that kind of activity of supporting groups that were targeting people he serves with every day in the Republican caucus," she said.
Collins is running for re-election but doesn't appear to be a target of the group for whom Cruz did the appeal.
Politico reported Wednesday that Cruz sent a fundraising letter on behalf of the Madison Project, a tea party organization that is working to help several candidates defeat veteran lawmakers in upcoming Republican primaries.
Those incumbents include Senate Minority Leader Mitch McConnell of Kentucky, Sen. Pat Roberts of Kansas, and Sen. Thad Cochran of Mississippi.
"I just would rather see us focus on Democrats," said another frustrated Republican senator who asked not to be identified. "I think when Republicans spend a lot of time and resources and effort defeating other Republicans it makes it that much harder to get to 51 in the Senate and that ought to be our goal."
Late last year, during another private GOP lunch following the government shutdown, the Texas Republican got an earful from several colleagues about whether he was involved with efforts by outside conservative groups, especially the Senate Conservatives Fund, to defeat incumbent Republicans.
Cruz promised his GOP colleagues he would not actively work to defeat them.
CNN asked Cruz about his decision to work on behalf of the Madison Project but he declined to comment and directed a reporter to his press staff for a response.
"The senator made an agreement last spring to sign the letter that the Madison Project put out. He remains supportive of their efforts for the conservative cause, and he stands by what he said about likely not getting involved in specific congressional incumbent races," said Catherine Fraiser, a spokeswoman for Cruz said in an email.
Cruz's fundraising was on the minds of several GOP senators as they left a private luncheon in the Capitol that Cruz attended Wednesday. But no one brought up the perceived infraction during the lunch and Cruz never spoke, according to several senators who attended the meeting.