The Quebec Federation of Labour (FTQ) is turning its back on the Bloc Quebecois.
The union's secretary general, Serge Cadieux, told La Presse that most union affiliates support the NDP.
He later told LCN that people should vote "for whichever candidate is best able to defeat the Conservative Party."
"We have to give our support to whichever party will defeat them."
Cadieux said that Tom Mulcair's party represents the values and demands that his own union is putting forward.
That's a statement that Liberal leader Justin Trudeau seems to agree with.
At the official opening of his campaign office in the Montreal riding of Papineau, Trudeau responded to a question about Cadieux's statement by saying "The FTQ is an openly separatist organization. It doesn't surprise me that it didn't choose to back the Liberal party, which is a real federalist party."
Trudeau could be trying to shore up support among federalists in Quebec, which is anticipated to be a battleground between the Liberals and NDP in the election, said McGill University political science professor Antonia Maioni.
"Mr. Trudeau is now playing the sovereignty card, which is a difficult thing to do in Quebec because most Quebecers want to move on from that," she said. "Like his father, he's not sympathetic of any form of Quebec nationalism and I think we'll see that played out in this election campaign."
In the LCN interview, Cadieux said he did not know of any single FTQ union shop that would be willing to support the Bloc, even though the union has supported the separatist party throughout most of its existence.
Earlier this year FTQ president Daniel Boyer said his organization would do whatever it could to get rid of the Conservative government led by Stephen Harper, and would be supporting whichever candidate in a riding was most likely to defeat the CPC.
With a file from The Canadian Press
