MP Jared O'Mara has been suspended by Labour while it investigates misogynistic and homophobic comments he is alleged to have made.
The Sheffield Hallam MP has apologised for online remarks from 2002 and 2004 but denies some more recent claims.
Labour initially said it would not be suspending the MP while these allegations were investigated.
But Jeremy Corbyn had decided to act when yet more comments emerged on Wednesday, a spokesman said.
Shadow chancellor John 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 who had defended Mr 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 He's been suspended, the whip has been withdrawn."
Asked about the case at Prime Minister's Questions, Theresa May said: "All of us in this House should have due care and attention to the way in which we refer to other people and should show women in public life the respect they deserve."
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 as a younger man.
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 did not 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.
The Guido Fawkes site has also found another post made by Mr O'Mara in his mid-20s, a review of an Arctic Monkeys gig, in which he calls women "sexy little slags".
And it has published details of a post to a music forum, allegedly made by Mr O'Mara in 2009, which includes offensive remarks about women.
Labour launched an investigation into Mr O'Mara's conduct on Tuesday, saying it was specifically looking at "comments and behaviour which have been reported from earlier this year".
But it has now said it is also looking at his online remarks from 2002 to 2004 and the newer alleged comments.
Labour's shadow education minister Tracy Brabin said Mr O'Mara's suspension was "probably a wise move".
Before the news broke, she had described his actions as "unpleasant and unacceptable", adding that the episode "doesn't look fantastic".
Conservative MP Mims Davies, chairwoman of the all-party parliamentary group for women in Parliament, said it was "right" that Mr O'Mara had been suspended over his "vile" comments.
But she added: "Why on earth has it taken so long?"
Pressed on why the party had waited until Wednesday to suspend Mr O'Mara, a Labour spokesman said the MP had gone to the Parliamentary Labour Party meeting on Monday night and made "a very thorough-going apology and talked about the journey that he'd been on. That was welcomed."
But "new information about things that he'd allegedly written more recently" had emerged, prompting Mr Corbyn to take action.
The Labour leader had made clear "this kind of abusive, misogynistic, sexist language is completely unacceptable and will not be tolerated in the Labour Party," he added.