By Alasdair Pal

SYDNEY (Reuters) -Unions at Woodside Energy Group's North West Shelf offshore gas platforms on Sunday announced plans to strike as early as Sept. 2, which could eventually disrupt shipments of liquefied natural gas (LNG) from top global exporter Australia.

The strike threat escalates a long-running dispute between Woodside and workers over pay and conditions on its North West Shelf gas platforms, which feed Australia's biggest LNG plant.

Unions in Australia are required by law to give companies seven working days' notice before any industrial action but can elect to call off any action before then.

The Offshore Alliance, which combines the Maritime Union of Australia and Australian Workers' Union, said in a Facebook post it had "unanimously endorsed" giving Woodside seven working days' notice to strike if its bargaining claims are not met by close of business on Wednesday. That would mean a strike could start as soon as Sept. 2.

"Woodside tried every tactic it could think of to avoid bargaining with its workers as a collective, but in the end the company failed to maintain the status quo it liked – one where what the company says goes," Offshore Alliance spokesperson Brad Gandy said in a statement.

"Offshore Alliance members don’t take industrial action lightly, but Woodside is really leaving them with little choice here."

A spokesperson for Woodside declined to comment on Sunday's update, referring to a previous statement that the company "continues to engage actively and constructively in the bargaining process".

Some 99% of Woodside workers granted unions permission to call a range of industrial action, including work stoppages, after Australia's industrial umpire, the Fair Work Commission, gave permission for "protected industrial action" to go ahead.

The Offshore Alliance also represents workers at Chevron's Gorgon and Wheatstone LNG facilities. Workers there on Friday began voting on whether to grant unions permission to call for strike action, with the first results due by Thursday.

Woodside's and Chevron's facilities together supply about 10% of the global LNG market. Concerns about a strike have spurred volatility in European gas prices over fears the move would fuel competition between Asian and European buyers for cargoes.

(Reporting by Alasdair Pal and Lewis Jackson in Sydney; Editing by Sonali Paul and William Mallard)