Married Labour MPs Ann and Alan Keen have been given a month to stop their local council repossessing their home 10 miles from the House of Commons.
The pair's expenses have been in the spotlight after they claimed £137,679 for a second home near Parliament.
In a letter seen by the BBC, Hounslow Council tells the couple "urgent action" is needed to explain why their main home in Brentford is unoccupied.
The Keens have not responded to BBC requests for a comment.
In addition, the Keens are not thought to have responded to the council's letter, sent last week.
A source at the council - which is run by the Conservatives - told the BBC that the Brentford property had remained empty for seven months.
Andrew Dakers, the Liberal Democrat councillor for the area, who is also its prospective Parliamentary candidate, has told the BBC that the windows at the back of the Keens main home were boarded up and that there was paint splashed on the inside of the upstairs windows.