The Government has officially registered its opposition to the 10% pay hike for MPs, amid growing pressure on David Cameron to block the increase .
A letter sent to the Independent Parliamentary Standards Authority (Ipsa) insisted the proposal for a salary bump to £74,000 is "not appropriate".
The row over the pay deal was triggered after Ipsa 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.
Shadow health secretary Andy Burnham, shadow home secretary Yvette Cooper and shadow care minister Liz Kendall have all declared they will forego the rise.
Education Secretary Nicky Morgan said she could increase the amount she gives to charity if the hike goes ahead, and a number of Tories are thought to be planning to donate the benefits. Other MPs are believed to have been asking Ipsa to introduce a mechanism that would allow them to "opt out" of the salary bump.
Mr Cameron previously described the £74,000 proposed pay packet, which comes at a time when the rest of the public sector is restricted to 1%, as "unacceptable".
But No 10 indicated earlier this week it would not seek to block the increase and refused to answer questions about whether the PM would give the money to charity.
The letter sent to Ipsa chairman Sir Ian Kennedy by Commons Leader Chris Grayling pointed out that the Government had provided a " comprehensive response" to the watchdog's initial consultation on the issue two years ago.
"The Government opposed the suggestion that there should be a pay rise of this nature at that time, and the view of the Government remains that a pay rise of this nature at this time is not appropriate," the letter said.
"You will be aware that as part of the Government's commitment to cutting the cost of politics, the Prime Minister has announced that we have frozen ministerial pay for a further five years, saving an estimated £4 million.
"While the Government notes the welcome economic indicators since December 2013 ... we continue to believe that despite the welcome signs of progress, the continuing structural deficit shows the job is far from done.
"The Government has an ongoing commitment to responsible fiscal policy and returning the public finances to a sustainable position."
The review 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 any more.
But MPs elected before 2015 - including Mr Cameron - will see a major boost to their pensions as they are based on final salary.
After trumpeting a "freeze" in ministerial pay last month, Mr Cameron is now in line for an effective 5% bump in his total remuneration, while Cabinet ministers' overall pay will increase by 5.2%.
Mr Cameron's total package will therefore rise by 5% this year, from £142,500 to £149,440.
A petition on the Change.org website calling for Mr Cameron to reject the Ipsa proposal as "unfair and unjust while Britain is going through austerity" has gained more than 365,000 signatures.