The union representing Detroit Three autoworkers in Canada has chosen General Motors as its target company as contract negotiations get serious.

Agreements reached between Unifor and GM will set the pattern for negotiations with Ford and Fiat Chrysler. However, the potential closure of GM's Oshawa assembly plant means a strike is almost inevitable if the automaker doesn't reverse course and offer up a big investment.

Each Detroit Three automaker has an endangered operation north of the border, including Ford's Windsor engine plant and, to a lesser degree, FCA's Brampton assembly plant (which builds the company's rear-drive cars). Oshawa's position is the most perilous, so it's no shock Unifor announced it will go after GM for commitments first.

Contracts will all three automakers expire on September 19. The union membership, which numbers 23,050, has already voted overwhelmingly for a strike mandate. Once members ratify an agreement with the target company, bargaining moves to the second and third company.

"Our demand is clear, invest today to build a future for tomorrow," Unifor president Jerry Dias told Canadian media today.

Recently, Dias called the negotiations the "most important auto contract talks in a generation." He promises "no deals with any of the companies without commitments from each of them for investments in Canada."

In late July, the Windsor Star quoted an unnamed GM Canada executive who claims that Oshawa's Consolidated Line is due to close next year. That assembly line manufactures Chevrolet Equinox crossovers in an overflow capacity. The same executive said the closure of the entire plant is not a "foregone conclusion."

Oshawa Assembly employs about 2,400 autoworkers building the Buick Regal and Cadillac XTS, in addition to overflow from GM's CAMI facility in Ingersoll, Ontario. In recent years, Oshawa lost its truck plant as well as the Chevrolet Camaro. Existing models produced in Oshawa could easily be sent elsewhere.

Last week, Unifor released an independent study showing the Detroit Three's $26 billion economic impact on the Canadian economy.

"Policy makers and the public need to understand what's at stake here," Dias said in a statement.

In the lead-up to contract negotiations, GM Canada refused to commit to the Oshawa plant's survival, though it did announce the province-wide hiring of 700 new engineers. That announcement raised eyebrows, with many believing it was meant to soften a looming blow to the company's Canadian workforce.