Labour has suspended senior MP Conor McGinn after a complaint was lodged against him.
The representative for St Helens North, in Merseyside, had his party membership administratively removed pending investigation, the PA news agency understands.
The move triggered the automatic removal of the Labour whip, meaning he will sit as an independent in the House of Commons.
Mr McGinn said he has not been told the details of the complaint but believes it is “entirely unfounded”.
Until recently he was a shadow minister without portfolio, playing a key role in preparing Labour for the next general election as deputy national campaigns co-ordinator.
In a statement reported by The Guardian, Mr McGinn said: “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.”