Labour MP Conor McGinn has been suspended from the party pending an investigation, the BBC has been told.
Mr McGinn, who has represented the St Helens North constituency since 2015, will now sit as an independent MP.
Details of the nature of the inquiry have not yet been confirmed.
In a statement given to The Guardian, Mr McGinn said “I strongly reject any suggestion of wrongdoing and I look forward to the matter being resolved quickly.”
“I have not been told the details of the complaint but I am confident that it is entirely unfounded.”
“The Labour party has informed me that it is automatically required to apply a temporary procedural suspension while a complaint is investigated.”
Mr McGinn – who has previously served as an opposition whip and the party’s deputy national campaign co-ordinator – is the latest Labour MP to be suspended under the party’s new complaints process.
The system was set up last year in the wake of controversy over how anti-Semitism allegations were handled.
A 2020 Equalities and Human Rights Commission report into how the claims were handled recommended that the party put in place “long-term arrangements for independent oversight of the complaint handling process”.
Party members backed creating this new system at its annual conference in 2021.
Under the rules, Mr McGinn’s suspension from Labour Party membership will lead to automatic precautionary suspension from the Parliamentary Labour Party.