The Commons Speaker has written to all MPs urging them to co-operate with the review of past expenses claims.
Hundreds of MPs are expected to be asked to pay back some of their claims following an investigation by Sir Thomas Legg.
The former senior civil servant was appointed by the Members' Estimate Committee (MEC) to look into claims from 2004 to 2008 after weeks of newspaper revelations about expenses.
He is writing to MPs on Monday to report back on his findings, and in a letter to MPs John Bercow said the investigation was "part of the important process of restoring public confidence in our allowance system and in the House".
The Speaker, who chairs the committee, added: "The MEC, therefore, urges members to co-operate fully with its inquiries."
The review has considered claims under the Additional Costs Allowance for each MP over the last five years, "with a view to ensuring that any overpayments are identified in order that they can be repaid".
"The next stage of Sir Thomas's work will be to ask each member who has received a letter raising issues for their view on his initial findings and, in some cases, to require more information where that is necessary," the Speaker wrote.
"Sir Thomas has said that there is an opportunity over the next three weeks for each member to respond to his letter.
"He will consider these responses prior to reaching his conclusion in respect of each member's claims. Sir Thomas will then submit his report to the MEC, which it will then publish and act upon."
It has been widely reported that hundreds of MPs, including the prime minister and other cabinet ministers, may be asked to repay money.
Liberal Democrat leader Nick Clegg is also being asked to return some of his claims. He has repaid £910 for gardening costs after he was advised to by Sir Thomas.
In his letter the Speaker reminded MPs that the Committee on Standards in Public Life under Sir Christopher Kelly will shortly be reporting on his proposals for the structure of a new system of allowances.
And the new Independent Parliamentary Standards Authority, which comes into operation next year, will manage an allowance system "which is wholly independent and in which members play no part".
Dods Parliamentary Communications Ltd