Unionized workers at Alcoa Corp.'s operations in Western Australia walked off the job after the aluminum giant asked regulators to terminate an existing enterprise bargaining agreement, Reuters reported Aug. 8, citing the Australian Workers' Union.

The company said the walkout has not impacted production as the sites have contingency plans in place.

The agreement affects about 1,500 of Alcoa's 1,600 workers at its three alumina refineries and two bauxite mines in the state. The refineries have a combined capacity of about 9.3 million tonnes, accounting for almost 8% of the world's alumina supply, according to Reuters.

Alcoa said that later in August it will ask employees to vote on a new agreement that will give them competitive pay and allow the company to be more efficient and productive.

The union said it negotiated for 20 months for a new agreement with Alcoa. The strike is not affecting Alcoa's Portland aluminum smelter joint venture in Victoria, according to the report.

The mines and refineries are owned by Alcoa of Australia Ltd., part of the Alcoa World Alumina and Chemicals Group, which is 60% owned by Alcoa Corp. and 40% by Alumina Ltd.

In Western Australia, the company's operations include the Huntly and Willowdale bauxite mines, part of the Darling Range assets, and the Kwinana, Pinjarra and Wagerup alumina refineries.