Australia is the world's biggest LNG exporter, and the ongoing dispute over wages and conditions had stoked volatility in gas prices. Gorgon and Wheatstone operations account for more than 5% of global LNG capacity.
"Despite the Offshore Alliance giving Chevron plenty of opportunity to sort out (bargaining agreements) ... they will finally be facing their day of reckoning," the union alliance said in a Facebook post. "It's game on, Chevron."
Chevron did not immediately respond to a request for comment.
Work stoppages that could reach up to 11 hours will begin from 1 p.m. Perth time (0500 GMT) on Friday and last through Sept. 14. A two-week total strike could then follow if the terms are not met, the union has said.
The strike action had been scheduled to begin on Thursday morning but was delayed due to mediation talks hosted by the Fair Work Commission, Australia's industrial umpire.
The stoppages, which had then scheduled to start on Friday morning, were later delayed until the afternoon, a Chevron spokesperson and a union representative told Reuters late on Thursday.
When strike actions begin, the LNG plant will have to be shut down "if there are not competent personnel to undertake handovers during work stoppages," the union said.
Although Australia is not a major supplier of LNG to Europe, British and European gas prices had been buoyed in recent weeks by the possible strike action on fears fewer Australian LNG cargoes going to Asia could lead to more competition for other sources of LNG and drive up costs.
China and Japan are the top two lifters of Australian LNG, followed by South Korea and Taiwan.
