Sometimes it's not what you say, but how you say it that matters most.

Anyone following the prime minister these past few weeks might just as easily conclude that it's not only what he says, but where he says it and to whom that matter most.

This week is a good case in point. Justin Trudeau gave a brief speech in Ottawa to the convention of Unifor, the country's largest private sector union, a speech interrupted by standing ovations that, once upon a time, would have been reserved for the leader of the NDP.

The prime minister knew that. It's why he was there. With a message of solidarity.

He began by saying the last election marked a new era in labour relations with the federal government. True enough, one supposes, if an era is defined by a decade of acrimony between unions and the former Conservative government.

He also had more to say, much more, about the connection between Liberals and unions.

Trudeau's NDP friend

Trudeau said his government believes that "Labour is a solution, not a problem." A copy of the speech capitalized the "L" throughout as though "Labour" was a formal name rather than a movement by and of working people.

He praised the work unions do holding employers to account, "and that includes my government," and for the leadership role Unifor and others have played in achieving fairness in the workplace for women, LGBTQ and Indigenous workers.

These are groups the prime minister has specifically identified as a central priority during his first year in office, groups who, once again, might have seen the NDP as a more natural political ally in the past.

Trudeau introduced Alberta NDP Premier Rachel Notley as his friend at the Unifor convention this week. (Codie McLachlan/Canadian Press) And just for good measure, Trudeau reminded the crowd they'd be hearing later from a friend of his, who just happened to be Alberta's NDP premier, Rachel Notley.

It's a mistake, of course, to assume union members vote NDP en masse. Or that the bond between labour and New Democrats has never been broken before.

Buzz Hargrove, as president of the Canadian Auto Workers, openly campaigned with Liberal Leader Paul Martin in 2004 and 2006. The CAW is one of the two unions that merged three years ago to create Unifor. The other was the Communications, Energy and Paperworkers Union of Canada, which represented several media organizations, but not journalists at the CBC.

Unifor was also a main force behind Engage Canada, the political action committee that ran attack ads against the Conservatives last year and supported strategic voting to oust the government.

Cement a new relationship

But it's no mistake that Trudeau is working hard this summer to cement a new relationship between his government and the New Democrats' traditional voting base.

It's one of the reasons the Liberal caucus retreat is meeting in Quebec's Saguenay region this weekend. The province is still home to 16 New Democrat MPs, and any comeback for the party that won 59 of the province's 75 seats in 2011 would likely start there.

Trudeau poses for photos as he flips a burger at a barbecue at the Liberal cabinet retreat in Sudbury, Ont., on Monday. (Nathan Denette/Canadian Press) The same can be said for the Liberals' choice of Sudbury for this week's cabinet retreat . The city has a large unionized workforce, and it's the heart of northern Ontario, a region where the NDP took votes and seats away from the Liberals in 2008 and 2011.

The Liberals are determined to starve New Democrats of the oxygen needed to breathe new life into their party. If it works, the odds of the Liberals holding on to seats taken from the NDP, and of winning another majority, look much better.

Playing up the friendship with Notley doesn't hurt either. She's come out with a plan to reduce Alberta's greenhouse gas emissions, while continuing to push for the approval of a pipeline — any pipeline — to get the landlocked province's oil to ports for export overseas.

Trudeau's speech to the union convention focused on many of NDP Leader Tom Mulcair's favourite themes. Pipelines might be anathema to environmentalists and the architects of the Leap Manifesto that doomed Tom Mulcair as NDP leader, but unions see the jobs such projects would create.

Trudeau didn't mention pipelines in his speech at the Unifor convention. Instead he played to the themes Mulcair said the NDP would promote as the third party in this Parliament: equality, social justice and fairness.

He reassured the crowd that his government would repeal the Conservatives' legislation that makes it more difficult for unions to organize in federally regulated workplaces.

His union audience responded with another ovation, which you might expect since Trudeau said exactly what they wanted to hear.