Three Labour MPs – including Jeremy Corbyn ally Chris Williamson – have been banned from standing for the party by its National Executive Committee.
Derby North MP Mr Williamson was suspended in an anti-Semitism row.
Jarrow MP Stephen Hepburn was being investigated over a sexual harassment claim – denied by him – while Roger Godsiff was facing a reselection battle in Birmingham Hall Green.
New candidates will be chosen to replace them.
Labour’s ruling National Executive Committee has not made a final decision on whether Keith Vaz can stand for the party, the BBC understands.
The Leicester East MP was last week suspended from the House of Commons for six months by a standards watchdog.
Mr Vaz “disregarded” the law by “expressing a willingness” to help buy cocaine for male prostitutes, the Commons standards commission said in a scathing report.
His Labour colleague, shadow home secretary Diane Abbott, said after the ruling that he should “consider his position”.
“I think he himself should agree not to be a candidate,” she told the BBC Radio 4 Today programme.
The MP did not make any comment on his suspension, but a spokesman said he was receiving treatment for a serious mental health condition.