(Bloomberg) -- Rio Tinto Plc. workers went on strike at an aluminum smelter in British Columbia on Sunday over labor contracts with the company, their union said in a release.

About 900 Rio Tinto workers at smelting facilities in Kitimat were on strike as of 12:01 a.m. Pacific time Sunday, Unifor said in a release posted on the union website.

“Our union is fully prepared to defend our members’ rights and protect good jobs in Kitimat now and in the future,” Jerry Dias, Unifor national president, said in the release.

The union’s bargaining committee negotiated until the strike deadline at midnight, Unifor said, accusing the company of violating existing contracts by using contractors and temporary employees and failing to address concerns over pensions and retiree benefits.

An email to Rio Tinto wasn’t immediately returned.

©2021 Bloomberg L.P.