An Illinois Republican on Monday said Sen. Scott Brown (R-Mass.) should be "ashamed of himself" for opposing Rep. Paul RyanPaul Davis RyanJuan Williams: Pelosi shows her power Cheney takes shot at Trump: 'I like Republican presidents who win re-election' Cheney allies flock to her defense against Trump challenge 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 CollinsEmanuel to take hot seat in Senate confirmation hearing Overnight Health Care — Presented by Carequest — FDA moves to sell hearing aids over-the-counter Rachel Levine sworn in as first openly transgender four-star officer in health corps MORE (Maine), announced she too would not vote for the plan.

Senate Majority Leader Harry ReidHarry Mason ReidHarry Reid calls on Democrats to plow forward on immigration Democrats brace for tough election year in Nevada The Memo: Biden's horizon is clouded by doubt 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.