By Renju Jose

SYDNEY Workers at Chevron's Gorgon and Wheatstone liquefied natural gas (LNG) projects in Australia plan a total strike for two weeks from Sept. 14, a union alliance said on Tuesday, a significant escalation on disputes over pay and conditions.

The decision comes amid mediation talks hosted by the Fair Work Commission (FWC), Australia's industrial umpire, which began on Monday and is scheduled to run every day this week, and ahead of brief work stoppages called by the union from Thursday.

"The Offshore Alliance is escalating protected industrial action to demonstrate that our bargaining negotiations are far from 'intractable'," the union alliance said in a Facebook post.

Australia is the world's biggest LNG exporter and the ongoing dispute has stoked volatility in natural gas markets with players nervous about the risk of long-term disruption.

Prolonged industrial action could disrupt LNG exports and increase competition for the super-chilled fuel, forcing Asian buyers to outbid European buyers to attract LNG cargo.

The union has already called for industrial action at the U.S. energy major's Gorgon and Wheatstone projects, which account for more than 5% of global LNG capacity, for seven days from Thursday Sept. 7, if parties cannot find a resolution.

Employees plan work stoppages of up to 11 hours in two blocks and will stop performing certain tasks until Sept. 14.

But in its latest update, the offshore alliance said the work bans could be extended until at least the end of the month. It said Chevron would be forced to finally agree to their terms "but not before they lose a few $Billion."

Chevron did not immediately respond to a request seeking comment outside of normal business hours.

Gorgon, Australia's second-largest LNG plant, has an export capacity of 15.6 million tonnes a year and Wheatstone 8.9 million.

(Reporting by Renju Jose in Sydney; Editing by Josie Kao and Sandra Maler)