Labour veteran Nick Brown has had the whip suspended following a complaint made against him.
The former Chief Whip, who has been an MP since 1983, has been placed on administrative suspension while the matter is investigated.
Mr Brown has also had his party membership suspended until the complaint is resolved. The details of the allegation are not known.
The Newcastle-upon-Tyne East MP told the Guardian : “There has been a complaint made about me to the Labour Party, which is under investigation.
"I am therefore under an administrative suspension from the Labour Party until the investigation is concluded.
"I’m not aware of what the complaint is.
"I am cooperating fully with the investigation."
Mr Brown has not been told what the complaint is about, according to the report.
Under Labour's independent complaints process, MPs have the whip suspended automatically while an allegation is under investigation.
Losing the whip temporarily means they cannot sit as a Labour MP during this time.
The former minister is one of Labour's longest serving MPs and served as Chief Whip under every party leader since Tony Blair.
He left the enforcer role when Keir Starmer reshuffled his top team last May, following Labour losses in the local elections and the disastrous Hartlepool by-election defeat.
The Labour Party declined to comment. Mr Brown was approached for comment by the Mirror.
