Workers at two of Chevron's major natural gas plants in Australia are set to go on strike next week, the US energy giant said Tuesday, threatening up to five percent of global LNG supplies.

Chevron has been told the strikes will start September 7 at its Gorgon and Wheatstone facilities in Western Australia, an announcement that has spooked markets already upended by Russia's invasion of Ukraine.

The company said it would "continue to take steps to maintain safe and reliable operations in the event of disruption at our facilities".

"We will also continue to work through the bargaining process as we seek outcomes that are in the interests of both employees and the company," it told AFP in a statement.

The Offshore Alliance, which represents Chevron's highly unionised workforce, said the strikes would "escalate each week until Chevron agrees to our bargaining claims" and that the company's efforts to date had been "inept and incompetent".

Strike action would cover some 500 staff and include "rolling stoppages, bans and limitations", the alliance added.

Union representatives said staff were looking to secure better pay, more flexible rosters, and enduring job security.

One of Europe's benchmark natural gas indexes jumped by about eight percent on Monday evening, as industrial action appeared to inch closer.

The Offshore Alliance has previously warned that it could "jam up" Chevron's operations, costing the company "billions in revenue".

Industrial action taken by Australian staff on Shell's Prelude gas ship lasted for 76 days last year, causing an estimated US$650 million in lost revenues.

The alliance has also accused Chevron of underpaying "highly skilled oil and gas workers engaged on remote major hazard facilities", and said it refused to be intimidated by the multinational energy giant.

- 'Knee-jerk reaction' -


Although Europe has largely replenished gas stockpiles disrupted by the war in Ukraine, there are fears that further disruptions, coupled with strong demand in Asia, could put the squeeze on supplies.

Saxo Markets analyst Redmond Wong said news of the strike could bring "knee-jerk reactions in European gas prices" -- but there was little long-term threat of gas running out.

Chevron is one of two major natural gas producers in Western Australia, alongside Woodside Energy.

Between them, the two companies account for more than 15 percent of international natural gas exports.

With capacity to produce more than 15 million tonnes of natural gas each year, Chevron is particularly proud of the Gorgon gas plant -- which it describes as "one of the world's largest LNG projects".

Natural gas prices spiked across Europe earlier this month after staff threatened industrial action at the offshore gas platforms owned by Woodside, with the same benchmark surging by more than 30 percent.

Those strikes were averted after the company managed to hammer out a last-minute agreement with union members.

Australia is one of the world's largest producers and exporters of natural gas.