CALGARY -- A union that represents workers in Canadian drywall factories is telling the prime minister a decision that could help the construction business might cost its members their jobs.

The International Brotherhood of Boilermakers have written Justin Trudeau asking that cabinet reject a trade tribunal's recommendation to relax anti-dumping duties that were imposed on imported U.S. drywall.

Earlier this month, the Canadian International Trade Tribunal found that American-made drywall dumped at less than normal prices into Western Canada over the past few years has hurt the Canadian industry.

The ruling called for replacing duties of up to 276 per cent that Canada imposed last year with permanent variable duties on any imports that fall below a floor price.

But the union says a recommendation that final duties be temporarily eliminated for a six-month period would hurt workers at gypsum board plants in Calgary and Winnipeg if the government approves the idea.

The union tells Trudeau that when preliminary duties were introduced, its members were rehired for a full shift at Calgary and an additional shift was introduced at Winnipeg.

"While your government has not accepted the tribunal's recommendations, the pessimism and expectation of continued unabated dumping have generated has already had an adverse impact on our members," says the letter to Trudeau, signed by Rob Lauzon, the union's assistant director of industrial sector operations.

The Western Canada Alliance of Wall and Ceiling Contractors applauded the tribunal's conclusion that the duties hurt consumers, and it called for a longer period than six months for the temporary elimination of final duties so that builders could fulfil their fixed-price contracts.

The duties were imposed after a dumping complaint by French-owned CertainTeed Gypsum Canada, the last drywall manufacturer in Western Canada with plants in Vancouver, Calgary and Winnipeg, and at two gypsum quarries, one in B.C. and one in Manitoba.

Fort McMurray mayor Melissa Blake said people who lost their homes in last year's devastating wildfire would suffer with a couple of thousand extra dollars in costs because of the drywall duties. Blake called for the federal government to offer grants to offset the impact of the duties.

The letter from the boilermakers' union says it supports duty relief for Fort McMurray, but that no Canadian worker should lose his or her livelihood to unfairly traded imports.

"There are no other good Canadian middle class jobs available for our members," the letter states.