Labour has suspended MP Geraint Davies pending an investigation into reports of “incredibly serious allegations of completely unacceptable behaviour”.
The decision to administratively suspend the Swansea West MP means he will have the whip removed in Westminster while a review is carried out.
It follows claims against the veteran politician, which were reported by the website Politico.
It reported that two female MPs had claimed Mr Davies, who has served in Parliament for 21 years over two spells, touched them inappropriately.
Politico said it had spoken to more than 20 serving MPs and Labour staff who described allegations of inappropriate behaviour stretching back at least five years.
It reported that the behaviour was directed exclusively at younger women in Westminster.
A Labour spokeswoman said: “These are incredibly serious allegations of completely unacceptable behaviour.
“We strongly encourage anyone with a complaint to come forward to the Labour Party’s investigation.
“Any complainant will have access to an independent support service who provide confidential and independent guidance and advice from external experts throughout the process.”
Labour is currently carrying out its own investigation into the claims made against Mr Davies.
Daniel Greenberg, the Parliamentary Commissioner for Standards, could also decide to open his own inquiry if he suspects the code of conduct for MPs may have been breached.
Mr Davies is also facing allegations that he “boasted” about bringing sex workers into Parliament for drinks.
Sky News, which reported the claims, cited an unnamed Labour MP who alleged that Mr Davies “would openly boast about bringing escorts and prostitutes onto the terrace and show them off”.
It is the latest set of claims made in what has been termed the “Pestminster scandal”, in which allegations of inappropriate sexual behaviour have been made against MPs or other senior figures in Parliament in recent years.
In 2021, Parliament’s watchdog, the Independent Expert Panel (IEP), found that former Hartlepool Labour MP Mike Hill committed two breaches of Parliament’s sexual misconduct rules in relation to his behaviour towards a woman in both his parliamentary office and his flat.
Mr Hill resigned as an MP before the panel could impose a sanction for his behaviour.
Former City of Chester Labour MP Christian Matheson quit in October after a report by the watchdog upheld complaints of “serious sexual misconduct”.
While Boris Johnson faced pressure due to the lockdown partygate scandal, it was Conservative complaints about his handling of assault allegations against former deputy chief whip Chris Pincher that led to his premiership collapsing last year.
Neil Parish, the former Tory MP for Tiverton and Honiton, sparked a by-election after admitting in April 2022 to watching pornography while in the House of Commons.
Shadow immigration minister Stephen Kinnock said Labour’s whips are “very alive” to the issue of sexual misconduct in Westminster.
He told Times Radio: “The key thing is that, when something like this happens, a formal complaint must be made.
“And I do genuinely believe that our whips and our party is very alive to this issue.
“People get suspended, they lose the whip, investigations take place.
“I think we need to make that happen as rapidly and effectively as possible and make sure that anyone who does feel that they have a complaint to make that they know that they can do so in confidence, and that they will be treated with respect and confidentiality and with action will be taken.”
Mr Davies has been contacted for comment.