An Illinois Republican on Monday said Sen. Scott Brown (R-Mass.) should be "ashamed of himself" for opposing Rep. Paul RyanPaul Davis RyanRubio discovers Native American heritage through TV show Feminine hygiene products to be available to House lawmakers using congressional funds Former Ryan aide moves to K street MORE's (R-Wis.) budget plan.

"Respectfully, Scott Brown ought to be ashamed of himself," Rep. Joe Walsh (R-Ill.) told Neil Cavuto on the Fox Business Network. "This is the defining moment of this generation. We have got to be bold. We know these entitlements have to be reformed to be saved. He knows that."

Walsh added that any Republican opposed to the plan was motivated by "political reasons."

"Any Republican that doesn’t vote for this or doesn’t support this is purely being guided by political reasons," Walsh continued. "This is not time to be politically scared. Every day I am in this town I am more convinced this president has no clue as to the financial cliff we are about to fall off of.”

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Walsh's comments come the same day that Brown, a centrist, penned an op-ed in Politico explaining why he won't vote for Ryan's plan.

"While I applaud Ryan for getting the conversation started, I cannot support his specific plan — and therefore will vote 'no' on his budget," Brown wrote in the op-ed.

Last month another centrist Republican, Sen. Susan CollinsSusan Margaret CollinsGOP braces for Trump's emergency declaration DOJ warns White House that national emergency will likely be blocked: report On The Money: Trump to sign border deal, declare emergency to build wall | Senate passes funding bill, House to follow | Dems promise challenge to emergency declaration MORE (Maine), announced she too would not vote for the plan.

Senate Majority Leader Harry ReidHarry Mason ReidKlobuchar: 'I don't remember' conversation with Reid over alleged staff mistreatment Dems wary of killing off filibuster Reid praises Warren, stops short of endorsement MORE (D-Nev.) is expected to hold a vote on the Ryan budget soon, perhaps as early as this week. Senate Democrats have charged that the Ryan plan is too extreme, particularly for its proposal to turn Medicare into a voucher system for Americans under 55.