Labour leadership hopeful Andy Burnham will not accept an inflation-busting 10% pay rise planned for MPs.
The £7,000 increase, which will take MPs' salaries to £74,000, has been proposed by the Independent Parliamentary Standards Authority (Ipsa).
Mr Burnham said if the planned hike goes ahead he will turn it down at source or donate the money to "local groups".
The shadow health secretary said the proposed rise "cannot be justified".
Ipsa has launched a final review of the plans, declaring it could see no "material" reason to change them.
Unless a consultation produces "new and compelling evidence" by the end of the month, the move will be confirmed, with the rise backdated to May 8.
The increase was originally unveiled in 2013 to address complaints that MPs' pay has dropped behind that for other jobs.
Writing on Twitter, Leigh MP Mr Burnham said: "I have always been clear that 10% pay rise for MPs cannot be justified. I won't accept it. Will turn down at source or give to local groups."
David Cameron is set to receive the £7,000 pay rise despite previously branding the increase "unacceptable".
Downing Street has made clear the Prime Minister will not seek to block Ipsa's proposal - and he will personally get the extra money.
It means that, having declared last month that ministerial pay was being frozen for the duration of the parliament, Mr Cameron is in line for an effective 5% bump in his total remuneration, while Cabinet ministers' overall pay will increase by 5.2%.
Downing Street said that although Mr Cameron still opposed the backdated increase in MPs' pay, it was ultimately a matter for Ipsa to determine.
The premier's spokeswoman said he was focused on areas where he had the power to bring down the cost of politics, including proposals for boundary changes to reduce the number of MPs at Westminster.
The government element of salaries has been frozen until 2020, but unlike in the last parliament, the rise for MPs will not be offset by cutting ministerial pay.
Mr Cameron's total package will therefore rise by 5% this year, from £142,500 to £149,440.
Blocking the rise for rank-and-file MPs would have required a change in the law, and with a slim majority it was far from clear whether Mr Cameron would have been able to carry a vote in the Commons.
The document issued by Ipsa stressed that due to cuts in pensions and expenses - such as a ban on claiming for evening meals - the overall package of changes will not cost taxpayers "a penny more".
Stella Creasy, one of the MPs seeking the deputy leadership, said she would also forego the extra pay.
"MP pay rise unjustifiable," she wrote on Twitter.
"If it goes through, will let my Walthamstow residents panel decide how to spend it on our local area."