UPDATE 2-Alcoa's W.Australia workers walk out over labour agreement - union

(Adds Alcoa comment, details)

KALGOORLIE, Aug 8 (Reuters) - Alcoa workers in Western Australia have walked out indefinitely over an enterprise agreement dispute with the aluminium maker, the Australian Workers’ Union (AWU) said on Wednesday.

The strike comes after Alcoa applied to Australia’s workplace regulator to terminate its current agreement, affecting around 1,500 of its 1,600 workers at its three alumina refineries and two bauxite mines in the state, the union said.

The refineries account for around 9.3 million tonnes of capacity or some 8 percent of the world’s alumina supply, with the market for the aluminium-making ingredient already tight after sanctions on global aluminium maker UC Rusal and the partial closure of Norsk Hydro’s plant in Brazil.

The walk out has not impacted production, Alcoa said.

The union said it spent 20 months trying to negotiate an agreement with Alcoa.

“Our members are sensible, and only want what is fair and reasonable – a secure and good job,” AWU WA State Secretary Mike Zoetbrood said.

“However, the members won’t accept the company using threats of termination as means of pressuring the workforce into accepting sub-par working conditions.”

Alcoa said it would ask employees to vote on a new enterprise bargaining agreement (EBA) later this month.

“Alcoa wants to establish a modern EBA that provides employees with competitive pay and conditions, allows us to manage our operations efficiently and productively, and gives us the ability to respond to changing market and operating conditions,” an Alcoa spokeswoman said in an email to Reuters. “Our sites have contingency plans to ensure they can continue to operate during industrial action,” she said.

Alcoa last year won regulatory approval to ship 2.5 million tonnes of West Australian bauxite to third-party customers, on top of the production it supplies to feed its Western Australian alumnina refineries.

That bauxite would go to China, where supply was already tight because the country’s pollution crackdown had closed some domestic mines, said Paul Adkins of aluminium consultancy AZ China.

Any disruption to West Australian supply could add more heat to China’s alumina prices, he added.

Alcoa’s aluminium smelter in Portland in the state of Victoria was not affected.

The refineries and mines are owned by Alcoa of Australia Ltd, which is part of the AWAC group of companies and owned 60 percent by Alcoa and 40 percent by Alumina Ltd. (Reporting by Melanie Burton; Editing by Christian Schmollinger and Sherry Jacob-Phillips)