A 50 per cent tariff regime would "shut down the entire North American auto industry," according to Unifor National President Lana Payne, whose union represents tens of thousands of Canadian autoworkers across the sector's Canadian footprint.

The warning lands as the industry faces the prospect of tariffs that would run directly through the cross-border supply chains that define North American vehicle production. Engines, transmissions, stampings and finished vehicles cross the US–Canada and US–Mexico borders multiple times before final assembly, and each crossing would compound the cost of duties at that rate.

Payne's framing is blunt: the North American industry does not operate as three separate national systems but as one integrated manufacturing platform. Tariffs set at 50 per cent would not simply raise prices on imported vehicles — they would break the production model itself, idling plants on both sides of the border.

Unifor speaks from a position of direct exposure. The union represents workers at the Canadian operations of the Detroit Three automakers — Ford, General Motors and Stellantis — as well as at parts suppliers and other manufacturing facilities tied to the vehicle sector. Canadian plants in Windsor, Oakville, Oshawa, Ingersoll and Cambridge feed directly into US assembly lines, and components built in US plants flow north into Canadian operations in equal measure.

The arithmetic behind the union's warning follows from how vehicles are built. A single finished vehicle can contain components that have crossed the border several times during production. At 50 per cent, tariffs applied at each crossing would multiply costs through the value chain rather than adding a single layer at the point of sale. Suppliers operating on thin margins would absorb losses first, with assembly plants downstream facing disruption as parts flows falter.

The threat extends beyond the OEM tier. Parts suppliers — many of them small and mid-sized operations concentrated in Ontario — depend on just-in-time delivery contracts with US assembly plants. A tariff wall at that level would render those contracts uneconomic, forcing production stoppages that would cascade from tier-two and tier-three suppliers up to final assembly.

Payne's statement also carries political weight in Canada, where the auto sector accounts for a significant share of manufacturing employment and export value. Ontario's auto industry alone anchors hundreds of thousands of direct and indirect jobs, and the union has been among the loudest voices pressing Ottawa for both a strong negotiating posture with Washington and support measures for affected workers and plants.

The union president's assessment contrasts with the framing of tariffs as a tool to reshore production. In Unifor's analysis, the integration of North American manufacturing is so deep that no single country could stand up replacement capacity quickly enough to avoid prolonged shutdowns. Plants idled by parts shortages would not reopen as relocated production — they would simply stop, with layoffs spreading through supplier networks and assembly operations alike.

What to watch next: whether Washington moves to implement tariffs at or near the 50 per cent threshold, how Ottawa responds with retaliation or support for Canadian plants and suppliers, and whether automakers begin announcing production shifts, downtime or investment delays in response to the tariff schedule.