The majority of almost 1000 workers have backed the action, which could threaten first gas at Gorgon, which is already months behind schedule and significantly over budget.

The workers for major contractor CB&I have offered to take a $8000 per annum salary cut in order to switch their rosters from 26 days on/nine days off, to a more family-friendly 20 days on/10 days off roster.

The Australian Manufacturing Workers Union and the Construction, Forestry, Mining and Energy Union say workers are open to further negotiations, but will take protected action, possibly starting with rolling strikes, initially for one hour a day, rising to 24 hours a day.

They may also refuse to complete paperwork.

Peak employer group, Western Australia's Chamber of Commerce and Industry, has warned the strike will further erode the state's reputation as an investment destination and could jeopardise future projects.

CEO Deidre Willmott said the unions' demands for more time off should have been matched with an offer to improve productivity.

"Many ordinary Australians would be envious of the high wages and generous working conditions these workers enjoyed before this strike action was pushed through," she said.

"As the majority of the resources industry is cutting costs in response to market conditions, people must be shaking their heads at this destructive and self-defeating industrial action."

She said if the action went ahead it would damage WA's ability to attract investment and put future projects at risk.

"Make no mistake, if the unions walk off the job it will not just hurt Chevron, it will make investors think twice about developing new resources projects in Western Australia which will hurt economic growth and job creation," Willmott said.

The Gorgon project is 90% complete, but may not meet its planned deadline of first gas sales before the end of the year.