The Scottish Labour leader has described Eric Joyce as unfit to stand again for the party, following allegations of an inappropriate relationship.
It follows a report in the Daily Record newspaper today alleging that the Falkirk MP formed a relationship with a 17-year-old girl who helped during his General Election campaign in 2010.
Johann Lamont, who is in charge of Labour MPs north of the border, said the 51-year-old had abused his position of power.
Joyce is also due in court next week charged with three counts of common assault following a fight in the Strangers Bar in the House of Commons on February 22.
Lamont said today: "If these reports are true, this sounds like a man who has abused a position of power and authority. I am disgusted. Regardless of other issues, I believe this makes him unfit to stand for Labour."
Joyce has denied the allegations that he had an affair. Speaking to the Evening Standardhe said the story was "not true" and that he was taking legal advice.
“I do know Meg and she did work for me during the election," he said. But he denied having a sexual relationship with her and said he had not seen her since the election.
A Scottish Labour Party spokesman said: "Eric Joyce was immediately suspended from the Labour Party when serious criminal charges were brought against him last week, so processes have already started.
"That case is now sub-judice but Eric Joyce remains suspended. These separate revelations are highly disturbing and Johann has made her position very clear."
Labour suspended Joyce from the party pending the results of the police investigation into the Commons incident, though he remains an MP.
Joyce, MP for Falkirk since December 2000, served in the Army Education Corps before pursuing a career in politics.