David Cameron is renewing his calls for the organisation that sets pay for MPs to rethink plans for a 10% salary hike.
Downing Street said a letter is being sent to the Independent Parliamentary Standards Authority (Ipsa) underlining the Prime Minister's opposition to the move.
Mr Cameron has come under pressure to take a stand against the salary increase after the frontrunners in the Labour leadership race made clear they will not pocket the cash.
He 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.
A Downing Street source said: "We're writing a letter to Ipsa to reiterate we stand by the detailed submission we had already made to them last year saying we think this rise is wrong."