Mr Jenkin says he will repay the money if necessary
Tory MP Bernard Jenkin has been asked to pay back £63,250 by expenses auditor Sir Thomas Legg.
It is the highest amount known to have been requested after an audit of MPs' claims on second homes expenses.
Mr Jenkin had claimed expenses to rent a property in his North Essex constituency from his sister-in-law.
He said the Fees Office was aware and he had not been told rules on renting from family had changed in 2006, but he would repay the money if he has to.
Downing Street asked Sir Thomas to review all MPs' claims under the controversial second homes allowance when the expenses scandal broke in May.
In the last few weeks about 600 MPs have received letters from him, seeking further information about claims, recommending some money be repaid, or telling them their expenses present no further issues.
He has also said there should have been annual limits on claims for gardening and cleaning - and recommended MPs who claimed more should repay the difference, although the claims were legitimate at the time.
But in Mr Jenkin's case the request relates to rent claimed on a property owned by his sister-in-law. MPs were banned from renting from relatives in 2006.
MPs were given three weeks to respond to the letters and it is understood that Mr Jenkin has responded and asked Sir Thomas to drop the demand because Commons authorities had sanctioned the arrangement and had not told him the rules had changed.
Mr Jenkin told his local newspaper, the East Anglian Daily Times: "I have pointed out that the House of Commons Fees Office was fully aware from the outset that this was a family arrangement.
"I have sent Sir Thomas copies of the letters and emails which show I sought to keep within the letter and spirit of the rules at all times.
"No question has been raised about my honesty, integrity or openness and I have reiterated to him that I will pay back whatever is finally recommended at the end of the process."
Gordon Brown has been asked to repay more than £12,000 he claimed - much of which relates to cleaning claims which exceeded Sir Thomas's retrospective limits.
The biggest amount known to be repaid by a single MP so far is £43,674 by minister Phil Hope.
He paid back the money in the summer, before the audit, after being criticised for the amount he spent refurbishing his flat. It was within the rules but he said his constituents' response had been a "massive blow".
Conservative sources told the BBC said Mr Jenkin's case was complicated and they would have to await Sir Thomas's final verdict.
Tory frontbencher Ken Clarke had been asked to repay £4,733 by Sir Thomas, but after making representations in writing to him he was told a mistake had been made and it should have been £1,345.