MP Conor McGinn has had the Labour whip suspended after a complaint to the party.
It is understood that the MP for St Helens North in Merseyside has also been administratively suspended as a Labour member while an investigation takes place.
The nature of the complaint is not yet clear, but McGinn has denied “any suggestion of wrongdoing”.
McGinn said in a statement: “The Labour Party has informed me that it is automatically required to apply a temporary procedural suspension while a complaint is investigated. I have not been told the details of the complaint but I am confident that it is entirely unfounded. I strongly reject any suggestion of wrongdoing and I look forward to the matter being resolved quickly.”
The Labour Party has declined to make any comment.
McGinn, 38, stood down as the party’s deputy national campaign coordinator in September to receive treatment for a heart condition.
He had been a key ally of Keir Starmer’s and was preparing to play a central role in Labour’s general election planning. He has previously served as shadow security minister and an opposition whip, having been elected to the seat in the north-west in 2015.