Labour MP Kelvin Hopkins has been suspended from the party "on the basis of allegations received", a spokesman said.
The MP, who represents Luton North, has had the whip withdrawn while an investigation into the claims is carried out.
Labour has not provided any details about the allegations, but ITV News understands they are historical in nature and were brought to the party's attention on Thursday by the alleged victim and The Telegraph.
It is alleged that Mr Hopkins "tightly hugged" a young activist at a Labour event at Essex University in 2014 and sent inappropriate text messages.
Labour said it takes complaints "extremely seriously" and has "robust" systems in place to deal with them.