Bury South MP and Labour former minister Ivan Lewis is facing an investigation following a complaint about his conduct, the party has said.
A party spokesman refused to discuss details of the allegation but said any complaint of sexual harassment was treated extremely seriously.
"The Labour Party takes all allegations of sexual harassment extremely seriously and all complaints are investigated in line with our robust procedures," the spokesman said.
"Ivan Lewis is currently under investigation following the receipt of a complaint."
Earlier this month the Bury South MP said in a statement he was sorry if his behaviour towards women he worked with had made anyone feel "awkward" but denied making any "non-consensual sexual comments or sexual advances".
It is understood that Mr Lewis has not been suspended by the party and continues to take the Labour whip.
Mayor for Greater Manchester Andy Burnham said: