Doncaster Central MP Rosie Winterton "reprimanded" a fellow Labour MP at the centre of sexual harassment allegations who went on to secure a promotion.
Kelvin Hopkins, the Labour MP for Luton North is currently suspended by the party over allegations he sent inappropriate text messages to a 27-year-old woman and rubbed himself up against her.
Now it has emerged that Dame Rosie spoke to Mr Hopkins about his conduct back in 2015 - but he later went on to be promoted to the shadow cabinet by leader Jeremy Corbyn.
Mr Hopkins, a former shadow minister until last year, has had the Labour whip withdrawn after a the investigation by the Daily Telegraph.
Ava Etemadzadeh said that she informed the whips office at the time of the incident and that a regional representative contacted the Leader’s office last year to raise concerns about the allegations.
A spokesman for the Labour Party confirmed that an investigation has been launched.
A statement said: “On the basis of allegations received by the Labour Party today, Kelvin Hopkins has been suspended from party membership, and therefore the Labour whip, while an investigation takes place.
“The Labour Party takes all such complaints extremely seriously and has robust procedures in place to deal with them.”
However, Ms Etemadzadeh, said she was angry that nothing appeared to have been done when she first came forward with the complaint.
Ms Etemadzadeh told the Telegraph that she met Mr Hopkins in 2013. The following year, she invited him to speak at a Labour event at Essex University, where she was Chair of the university's Labour society.
She alleges that after the event, when she was 24, he hugged her very tightly and rubbed his crotch against her.
"He hugged me to say goodbye, held me too tight and rubbed his crotch on me, which I found revolting, she said. Over the following months, she was sent a number of "inappropriate" text messages by the Labour MP.
In December 2015 she said that she contacted the whips office about Mr Hopkins’ behaviour.
It is understood that at the time, Mr Hopkins was spoken to about why his behaviour was inappropriate and was reprimanded by Dame Rosie.
But he went on to be promoted, albeit briefly, to Labour's front bench in June 2016 - shortly after leader Jeremy Corbyn faced mass resignations following the EU referendum.
Sources suggested Labour whips advised the leader's office not to promote him because of what happened. The leader's office say that is not the case.
She 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."