Labour has suspended Luton North MP Kelvin Hopkins after an allegation, believed to be of sexual harassment, was received by the party.
The party has not given any details of the nature of the claims but the BBC understands it relates to an incident first reported a couple of years ago.
Mr Hopkins has had the whip withdrawn while an investigation takes place.
A party spokesman said Labour “takes all such complaints extremely seriously and has robust procedures in place”.
The backbencher – who was shadow culture secretary between July and October 2016 and has been Luton North MP for 20 years – could not be reached for comment.
Labour sources say a complaint of sexual harassment was made against Mr Hopkins a couple of years ago.
It was handled internally and the MP was reprimanded at the time, the BBC understands.
However, new allegations have been made about the same incident this week.
It comes amid various claims of sexual harassment in Parliament, which saw the Conservative Sir Michael Fallon quit as defence secretary on Wednesday night.