The general secretary of bakers' union BFAWU - which is affiliated to Labour - has revealed he has been suspended from the party.
Ronnie Draper said he has also been told he cannot vote in the upcoming leadership election.
Taking to Twitter, Mr Draper - whose union supports incumbent leader Jeremy Corbyn - said he had been a member for most of his life.
He said he was "disgusted and in shock" after receiving the letter informing him of his suspension, pending a hearing.
He said it was down to something he wrote on social media.
Meanwhile, a number of other Labour party members said they had also been suspended today.
One person claimed that four people with a combined membership of 163 years had all received letters. Another said his application to join had been rejected on the grounds that he had tweeted support for the Green Party.
Labour said it could not comment on individual cases.