Labour is widening its inquiry into allegations of anti-Semitism among its university organisations, the BBC understands.
Labour peer Baroness Royall is looking into claims of anti-Semitism at Oxford University Labour club, as part of a review of Labour's youth wing.
She will now also consider a complaint relating to a Labour student at LSE, it is understood.
MP John Mann called on leader Jeremy Corbyn to take "decisive action".
He told BBC One's Sunday Politics: "It's not a big problem, but a small problem when it comes to racism needs to be dealt with."
The complaint at LSE - London School of Economics - relates to student Rayhan Uddin, who is in the Labour group there and recently ran for election as the student union's general secretary.
He was criticised for a Facebook post that emerged during the campaign in which he wrote that "leading Zionists" wanted to take over the student union to "make it right wing and Zio again".
Mr Uddin has since apologised "unreservedly" for his use of language, saying it is "utterly repugnant to me to think I may have unwittingly appeared to endorse in any way the foul ideology of anti-Semitism".
The BBC has contacted Mr Uddin for a comment but he has declined to be interviewed.
On the Sunday Politics, Mr Mann, who chairs the all-party parliamentary group against anti-Semitism, said there was "no space for anti-Semitism" in the Labour movement.
"We cannot tolerate a situation where any part of society doesn't feel that a major political party like the Labour Party is not the place for them, which is why prompt effective action and vigilance on this is required, including from Jeremy," Mr Mann said.
Asked whether Mr Corbyn was doing enough, he said it was "clear" the leader "does not tolerate or support" anti-Semitism.
But he added: "What he has to do is follow that through with actions and ensure that others in the Labour Party follow it through with actions.
"Because the kind of thing and the atmosphere that's been created in Oxford University is not a one-off. This has been happening elsewhere as well."
The Bassetlaw MP likened the situation to 30 years ago, when extremists tried to ban student Jewish societies in some universities.
"Some of that's crept into the Labour Party and it needs to be removed," he told the BBC.
'Words not enough'
Asked what had caused the apparent resurgence in anti-Semitism, Mr Mann pointed to an increase in the party's membership and said that some new members "have attitudes that are very outdated - they're prejudiced".
He said Labour's internal inquiry needed to lead to "decisive action", saying "there are many of us who will only accept the highest standards... words aren't good enough".
The Parliamentary Labour Party is currently carrying out an investigation into allegations of anti-Semitism in the Oxford University Labour Club.
Alex Chalmers resigned as club co-chairman last month after it voted to support Israel Apartheid Week.
Oxford University Labour Club has said previously in a statement: "We are horrified at and whole-heartedly condemn anti-Semitic behaviour in all its forms."