MASCOUCHE, Que. -- A major and sovereigntist-leaning labour federation in Quebec has dropped its long-standing endorsement of the Bloc Quebecois and some of its member unions are supporting the NDP, making party leader Tom Mulcair "extremely proud."

Mulcair said New Democrats will work hard to maintain support from Quebec's unions -- who have traditionally supported sovereigntist parties at the federal and provincial levels -- in order to "expand our traditional base and rally progressives across Quebec and Canada."

Quebec's FTQ federation is heavily involved in politics; it covers 37 labour unions and counts 600,000 members.

Its secretary-general, Serge Cadieux, said Tuesday the FTQ is not officially endorsing any political party, but that two of its unions have so far come out in support of the NDP.

The federation has officially endorsed the Bloc in almost every federal election since the early '90s and it favours the sovereigntist Parti Quebecois provincially.

This time, however, Cadieux said the Bloc is not best-placed to beat the Conservatives, whom he called "catastrophic" for working people.

Cadieux said the FTQ has targeted 10 ridings in Quebec where support for the Conservatives is relatively strong and where it will "focus its energies."

The plan is to endorse and help any candidate in those ten ridings who has the best shot at beating a Tory, whether they be affiliated with the Liberals, NDP, Bloc or the Green party, Cadieux said.

Bloc Leader Gilles Duceppe downplayed the news Tuesday, saying that the FTQ has been planning to drop its support for the Bloc for a while.

"The (FTQ) is not endorsing any specific party," he said in Quebec City. "It will support candidates in 10 ridings...We've known that for a year."

Conservative Leader Stephen Harper's Quebec Lieutenant, Denis Lebel, took to Twitter on Tuesday and slammed the NDP saying "the last thing the country needs is an NDP government at the mercy of unions."

Liberal Leader Justin Trudeau said he wasn't surprised that an "organization that is openly and officially sovereigntist" chooses to support the NDP rather than his, "truly federalist" party.

The NDP leader brushed off suggestions that support from a large and powerful labour federation that has historically supported the separatist Bloc would hurt the party's image outside Quebec.

Mulcair said the NDP is a big tent that welcomes all Quebecers, even if some of them have supported the sovereigntist cause in the past.

"That's the beauty of the NDP's offer to Quebecers," he said during a campaign stop at a pre-fabricated house company in Mascouche, Que., about 40 kilometres north of Montreal.

"We want to go beyond the old quarrels of the past."

Mulcair also visited a family dairy farm Tuesday in Danville, Que., about 160 kilometres southwest of Montreal, and said if elected, he would create a payment-protection program for farmers who don't get paid if they sell their products to U.S. companies that go bankrupt.

Mulcair also said he agreed to participate in a bilingual debate on foreign policy hosted by The Munk Debates on Sept. 28.

There are two other debates scheduled, one by the Globe and Mail and another by French-language broadcaster TVA. Mulcair said he'd participate in the TVA debate but would only confirm the Globe one if Harper agreed to take part in a second, French-language debate.

Mulcair is scheduled to spend Wednesday in the Quebec City area, where the party says it can maintain its seats and take others away from the Conservatives, who have strong support in the region.