The agreement covers about 600 employees represented by the United Steelworkers union.
USW Local 1005 reached a tentative agreement with the company last week. It says the contract was accepted by 86 per cent of the votes cast, with 77 per cent of the membership represented.
The contract comes as the Canadian arm of Pittsburgh-based U.S. Steel operates under court protection while the company attempts to reach a compromise with its creditors.
The agreement runs until the end of March 2017, essentially extending terms of a labour agreement that expired on Oct. 15.
U.S. Steel Canada — which owns the former Stelco operations — employs about 2,000 people at the Hamilton Works in Hamilton and Lake Erie Works in Nanticoke, Ont.
"The extension of the agreement with USW Local 1005 sends a strong message of stability to the suppliers and customers of U.S. Steel Canada. Our customers will continue to have a source of high quality steel supply while the company restructures, without concern of a work stoppage," said William Aziz, U.S. Steel Canada's chief restructuring officer.