TORONTO -- Canada's largest provincial labour federation says it is ready to launch its "Dump Harper" campaign as soon as the prime minister calls an election, which is widely expected to happen on Sunday.

The president of the Ontario Federation of Labour said Friday that the move will mirror the "Stop Hudak" campaign against former Progressive Conservative leader Tim Hudak in the provincial election last year.

Sid Ryan said the union will engage members in what he called "vulnerable" ridings across the province where the races are expected to be close.

"A union drive in our workplaces to drive down the Conservative vote could be very, very effective and could be the difference between wining and losing," Ryan said.

The OFL's "Stop Hudak" effort drove down the Tory vote among the group's members from 30 per cent to 19 per cent, Ryan claimed in an interview.

Hudak stepped down as party leader after the provincial Liberals secured a majority despite a legacy of scandal. He ran into trouble with a promise to cut public-sector jobs at a time when the provincial economy was sputtering, drawing the ire of many in the labour movement.

The latest campaign, if successful, could have a significant impact on the upcoming national vote as Ontario accounts for more than one third of the 338 seats that will be up for grabs in the upcoming federal election.

Ryan says the races the OFL plans to target include ridings in Oshawa, London, Welland and Hamilton -- all communities where there is a significant labour movement.

"There's a million unionized workers in Ontario and they're concentrated in some key ridings," said Ryan. "We've already had meetings with local union leaders and their job is to go back into their workplaces and talk to their members."

Ryan said the OFL would reach out to people who were in leadership roles in their local unions to ask them who in their workplaces was likely to vote Conservative.

Those community leaders would then be given a "tool kit" to help them in their conversations with anyone with Tory tendencies, he said.

The OFL's mandate is to support the NDP, but Ryan noted that the priority in the upcoming campaign will be to discourage votes for the Conservatives.

The campaign is expected to be mirrored by the national Canadian Labour Congress in other provinces across the country, Ryan said.

"We've already been out having area meetings all across Ontario," said Ryan. "If (Harper) drops the writ tomorrow, labour will kick into high gear. Simply all of our energies in the labour movement will now be focused in on this election to make certain Harper does not get into government."