MONTREAL – The federal government and members of Canada’s aluminum industry are expressing frustration over an effort to impose a 50 per cent tariff on aluminum imported into the U.S., most of which comes from north of the border.

The United Steelworkers union filed a petition Monday with the U.S. International Trade Commission that aims to stem the flow of imported primary unwrought aluminum it claims has decimated the American industry and jobs. About 6,500 workers in the U.S. aluminum sector have been laid off since 2011, when production was four times the volume it is today…