Labour has suspended Luton North MP Kelvin Hopkins after it was alleged he sexually harassed a party activist.
Ava Etemadzadeh told the BBC that she made a complaint about the incident two years ago.
The party has not given any details of the claims, but Mr Hopkins has had the whip withdrawn while an investigation takes place.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 suspension came minutes before the Telegraph published details of the allegations, in its online edition, put forward by Ms Etemadzadeh.
BBC political editor Laura Kuenssberg said there had not yet been any comment from Mr Hopkins – who has been Luton North MP for 20 years – despite repeated attempts to contact him.
The backbencher was asked to join the shadow cabinet as shadow culture secretary in June 2016 – after a complaint of sexual harassment had been made against him, according to Labour sources.
It was handled internally and the MP was reprimanded at the time, the BBC understands.
Ms Etemadzadeh said she made the allegation before his promotion but was told she “couldn’t take anonymous action”.
Sources suggested the whips advised the leader’s office not to promote him because of what happened. The leader’s office say that is not the case.
Ms Etmadzadeh told the BBC: “I was shocked to learn that he got promoted afterwards.
“I’m disillusioned by the party not just not doing anything, but then promoting him afterward. They ignored it.”
New allegations have been made about the same incident this week.
The BBC has been told that Ms Etmadzadeh had a meeting with the chief whip on Thursday. That has not yet been officially confirmed.
The suspension comes amid various claims of sexual harassment and improper behaviour in Parliament.
Sir Michael Fallon quit as defence secretary on Wednesday night, saying his conduct may have “fallen short” of the standards expected by the UK military.
In another incident, Labour confirmed it had launched an independent inquiry into claims that activist Bex Bailey, 25, was discouraged by a party official from reporting an alleged rape at a Labour event in 2011.
Party leaders have vowed to tackle discipline and grievance procedures.
In a letter to Commons Speaker John Bercow, Theresa May said disciplinary procedures needed to be reformed.
The current system for airing grievances was not fair on employees, she said.
On Wednesday, Labour said that there must be “robust procedures” inside as well as outside Parliament for dealing with abuse and harassment.