Rochdale MP Simon Danczuk has condemned "poorly worded" expenses rules which punish "modern families" after an investigation was launched into his accommodation claims.
The divorced politician is alleged to have received thousands of pounds in funding to have his children stay with him in London - even though they hardly ever visited his flat.
The Independent Parliamentary Standards Authority (Ipsa) allows MPs to claim an extra £2,425 a year towards accommodation costs for each dependant.
The system gives them scope to rent a flat with more than one bedroom, and means they can "maintain contact with their families during the course of their parliamentary work", according to the watchdog.
But Ipsa compliance officer Peter Davis has announced a formal probe into Mr Danczuk after a member of the public complained that the rules were being abused.
Mr Danczuk, who has been suspended by the Labour Party over separate allegations, has two children with first wife Sonia Rossington, and two with second wife Karen Danczuk.
His 18-year old son George told the Rochdale Online website last week he stayed with his father in London just once, in February 2012.
"That's the only time I've stayed with him in London," he said.
In a statement Mr Danczuk said: "My original claim was made properly and based on my honest interpretation of the Ipsa regulations.
"I maintain that the existing rules are poorly worded and not fit for purpose when it comes to modern families like mine.
"Some of my Parliamentary colleagues have approached me in the last week to say they agree with me on this point and that they have interpreted the rules the same way.
"I'll be meeting with the chief executive of Ipsa about this and I will stress the need for the system to be more flexible to reflect the living arrangements of modern families.
"I am co-operating fully with the investigation and welcome the chance to get this matter cleared up."
Police are thought to have declined to investigate the allegations.