Seven of the 10 Bloc Quebecois MPs quit Wednesday because of Martine Ouellet's leadership style, leaving the once-powerful party in complete disarray.
The seven, who will sit as Independents, made the announcement after a Bloc caucus meeting in Ottawa.
One of them is Louis Plamondon, who has been in the Commons since 1984, including the last 25 years as a Bloc MP.
Plamondon said he is "leaving the leader" but "is not leaving the Bloc Quebecois."
The departures are a crushing blow to a party that formed the official Opposition under Lucien Bouchard in 1993.
Gilles Duceppe then took over the reins of the party and led it in five consecutive elections in which it won at least half of the seats in Quebec.
Duceppe also guided the party in the 2011 and 2015 elections, leading them to only four and 10 seats respectively.
The six other MPs who are leaving the Bloc caucus are Luc Theriault, Gabriel Ste-Marie, Rheal Fortin, Michel Boudrias, Simon Marcil and Monique Pauze.
Ouellet, who does not have a seat in the Commons, is a former Parti Quebecois cabinet minister who is still sitting in the Quebec legislature as an Independent.
She became Bloc leader last March.