Jeremy Corbyn could be investigated over whether he has broken the MPs' code of conduct by not declaring financial and "in-kind" support for legal disputes.
Labour MP Neil Coyle, a critic of Mr Corbyn, has written to parliament's standards commissioner claiming Mr Corbyn may have not declared support he has received to cover legal costs, mostly regarding the fallout from claims of antisemitism in the Labour Party.
Mr Coyle said: "All MPs are expected to follow certain rules and some people seem to think they're above it.
"We expect it from Boris Johnson with flat refurbishments, childcare and foreign holidays. But we cannot attack the Tories if we don't equally take action when someone who seeks to be a Labour MP is receiving significant financial support and contributions, and not declaring it."
In response, Jeremy Corbyn has told Sky News: "I will be liaising with the commissioner in response to Neil Coyle's correspondence."
In January, Mr Corbyn lost a court battle to force Labour to hand over documents relating to his suspension from the parliamentary party. It is understood Labour intends to recover its costs from Mr Corbyn.
In March, the former Labour leader lost an appeal against a High Court decision in a libel fight brought by a political blogger.
Mr Corbyn's register of interests details he is "likely to benefit from a legal fund managed by JBC Defence Ltd which was set up on 16 October 2020 to help meet any legal costs which I or my supporters incur in relation to allegations of defamation". It is not clear who has contributed to this fund.
Jeremy Corbyn was suspended from Labour in October after his response to a critical report on antisemitism within the party.
He claimed the scale of Labour's antisemitism problem was "dramatically overstated" by opponents.
Mr Corbyn's membership was reinstated within weeks, but the Labour whip was not restored meaning he is not a member of the Parliamentary Labour Party (PLP) and remains an independent MP.
The parliamentary commissioner for standards has declined to comment.