Labour MP Nick Brown has been temporarily suspended from the party pending an investigation, it is understood.
In accordance with the Labour Party's rules, Mr Brown's administrative suspension means he has automatically had the whip suspended as a precaution.
The Guardian reported that a complaint had been made against the member for Newcastle-upon-Tyne East, who has previously served as Labour chief whip.
But the newspaper said the nature of the complaint is unknown.
Sky News has approached Mr Brown for comment.
The 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 been an MP since 1983 and is the fifth-longest serving member of the commons.