An overwhelming 99% of Offshore Alliance members have voted to strike at Woodside Energy's Pluto LNG 2 facility, according to results released on the organisation's Facebook page on Thursday.
Around 400 members of the Electrical Trades Union also voted at close to 99% for protected industrial action - a legal strike - the union said separately.
Workers' representatives will now go back to members to discuss what form the action will take.
A strike could slow work at Pluto 2, a 5-million-metric-ton expansion of an existing facility in Western Australia's Pilbara region. Woodside hopes to ship its first liquefied natural gas cargo from Pluto 2 in the second half of 2026.
The Offshore Alliance is seeking a 30% pay rise, saying workers at Pluto 2 are receiving 30% less per hour than workers previously did doing the same job at the Wheatstone LNG project operated by Chevron.
The Alliance, comprising the Maritime Union of Australia and the Australian Workers Union, said in November that salary negotiations with contractor Bechtel had gone nowhere and the next move was to strike.
The ballot results had not been made public on the FWC website at the time of writing. The Commission approved a ballot in late November, several days after unions applied for protected industrial action. The Electrical Trades Union and two other unions also applied for PIA and won the right to ballot members.
Bechtel had argued against allowing the ballot of Offshore Alliance members, and has said the Alliance should not be encroaching on more traditional onshore construction work.
(Reuters - Reporting by Shivangi Lahiri in Bengaluru and Helen Clark in Perth; Editing by Mrigank Dhaniwala and Philippa Fletcher)