7 Bloc Québécois MPs

Seven of the Bloc's ten MPs left the party to protest their leader Martine Ouellet. They formed a temporary group called Québec debout. It was an organized revolt - 70% of the caucus left at once.

Their revolt worked. Ouellet lost a leadership review vote, and all seven MPs eventually returned to the Bloc. This is a case where crossing the floor was used as a weapon to remove a leader - and it succeeded.