Labour has launched an investigation into MP Jared O'Mara's comments and behaviour following claims he called a constituent an "ugly bitch" just months before his election.
Mr O'Mara "categorically denies" the claim made by his Sheffield Hallam constituent Sophie Evans about an incident in March this year.
On Monday Mr O'Mara resigned from his position on the Commons Women and Equalities Committee in a row over homophobic and sexist online comments posted more than a decade ago.
Newly revealed online comments from the same period show he also made derogatory remarks about the Spanish and Danes.
Labour said the investigation into Mr O'Mara related to the allegations from this year.
"The party is investigating Jared O'Mara MP in relation to comments and behaviour reported from earlier this year," a spokeswoman said.