Police are being urged to investigate former coalition minister Mark Harper after he admitted employing an illegal immigrant as a cleaner.
Labour backbencher John Mann has written to Scotland Yard commissioner Sir Bernard Hogan-Howe asking for a probe into whether the law was broken.
Mr Harper resigned over the weekend after admitting he had failed to make sufficiently rigorous checks on his cleaner's status. The Tory had been responsible in the Commons for the Immigration Bill - which among other changes seeks to double the fines on employers who recruit illegal immigrants to £20,000 per case.
Prime Minister David Cameron said he accepted the resignation "with regret". Today Theresa May described Mr Harper as an "excellent minister" and dismissed the idea that he had broken the law.
"Mark has said very clearly that he felt he should hold himself to a higher standard," she told BBC Radio 4's Today programme.
But Mr Mann said: "I have referred Mark Harper to the police as legal experts are suggesting that by employing an illegal immigrant and failing to keep the relevant documents, he may well have broken the law.
"The idea of Harper's resignation being 'honourable' is nonsense.
"As Immigration Minister, he claimed more than £2,000 in expenses from the taxpayer to pay an illegal immigrant to clean his home and iron his clothes.
"I have already called for Mark Harper to reject the £8,000 payoff he can expect after quitting.
"That however is not enough - the case clearly warrants a full police investigation."
The Independent Parliamentary Standards Authority (Ipsa) banned MPs from claiming cleaning of second homes on expenses in 2010, so Mr Harper has not funded cleaning through allowances since becoming a coalition minister.
Asked how Government ministers had come to the conclusion that Mr Harper had not broken the law, Prime Minister David Cameron's official spokesman said: "It was on the clear advice the Government had received from Home Office lawyers."