Celebrity Big Brother housemates Traci Bingham, Rula Lenska and Maggot are up for eviction after being nominated by George Galloway and Samuel Preston.
Preston said Bingham had ostracised herself from the group.
The MP and singer cast their votes unaware they were being watched by the rest of the house.
The public can vote against the three until 2100 GMT on Friday. The housemate with the most votes will be evicted.
Former Football Association secretary Faria Alam was voted off the Channel 4 reality TV show on Wednesday.
Glamour model Jodie Marsh left last Friday.
Galloway and Preston were called into the diary room and asked to nominate three housemates after discussing nominations - in breach of one of Big Brother's fundamental rules.
They were watched by the other celebrities on a plasma screen.
Once they had left the room, former basketball star Dennis Rodman congratulated the pair on the way they had handled themselves.
Nine stars, including former TV host Michael Barrymore, singer Pete Burns and one unknown contestant planted by producers - Chantelle Houghton - are still in the fourth series of the show.