Liquefied natural gas workers at key Chevron Corp. sites in Australia began partial strikes Friday after talks failed to reach an agreement in a dispute that’s roiled global gas markets.

European benchmark gas prices jumped as much as 11% on the news, highlighting the market’s vulnerability after last year’s energy crisis. Partial strikes began at 1 p.m. Perth time at the Gorgon and Wheatstone facilities, which accounted for about 7% of global LNG supply last year.

Members of the Offshore Alliance union said they will stop work completely for two weeks starting Sept. 14.

Read more: How LNG Strikes in Australia Will Impact Natural Gas Supply

The start of the industrial action marks the culmination of weeks-long discussions that have kept global gas markets on edge. Unions first threatened to pursue strikes at the Chevron sites and Woodside Energy Group Ltd.’s facilities in early August. Since then, Woodside reached a compromise deal with workers, while Chevron and its workers remain apart on several key claims.

Friday’s partial strikes include work stoppage and bans on carrying out overtime and some other duties.

Chevron’s “bargaining performance has been the most inept effort of any employer the union has dealt with in the past five years and our members have had enough,” Offshore Alliance said in a post on Facebook earlier on Friday.

The impact on LNG shipments isn’t likely to be immediate, and gas consumption is currently muted in both Europe and Asia. Still, the prospect of disruptions to future supply has sent prices higher as it threatens greater competition for cargoes during peak demand in the northern hemisphere winter.

Friday’s initial strikes “appear lower level, designed to create costs and inefficiencies for Chevron, but not yet impact production materially,” said Saul Kavonic, an energy analyst at Credit Suisse Group AG.

--With assistance from Elena Mazneva.

(Updates with details throughout.)