Jared O’Mara has been suspended by Labour while it investigates comments he allegedly made, Shadow Chancellor John McDonnell has said.
The Sheffield Hallam MP, who was elected this year, faces claims he made misogynistic and homophobic remarks.
He has apologised for remarks made online in 2002 and 2004, but denies some more recent allegations.
The party is investigating “comments and behaviour which have been reported from earlier this year,” it said.
On Monday, Mr O’Mara resigned from the women and equalities committee after political website Guido Fawkes unearthed offensive comments made by the 35-year-old MP online some time ago.
Then on Tuesday, Sophie Evans told the BBC’s Daily Politics she had met Mr O’Mara on a dating app and there had been “no hard feelings” when things didn’t work out between them.
But in an incident in March, Mr O’Mara, who was DJing in a nightclub, made comments to her that “aren’t broadcastable” and called her an “ugly bitch”, she said.
A spokesman for Mr O’Mara said the MP “categorically denies” the allegation.
Mr McDonnell told the BBC: “There will be a full investigation by the Labour Party and then, as a result of that, a final decision will be made about his future.”
Asked about Labour colleagues that had defended Jared O’Mara in recent days, Mr McDonnell said: “They were basing that judgement on the information they had before them and the information that was provided to them by Jared himself and others.
“New information has come to light, so quite rightly the Labour Party has acted swiftly, he’s been suspended, the whip has been withdrawn.”
Labour’s Shadow Education Minister Tracy Brabin said the party’s suspension of Mr O’Mara was “probably a wise move”.
Before the news broke, she had described Mr O’Mara’s actions as “unpleasant and unacceptable”, adding that the episode “doesn’t look fantastic”.
Also reacting to Mr O’Mara’s suspension, the Conservative MP Suella Fernandez said: “A suspension is more than words, and that is the appropriate course of action.”