The boss of one of the state's most powerful unions has delivered a stinging rebuke to the McGowan Government for giving the green light to fracking in the North West and has promised to recruit branch members into the Labor Party to fight the decision.

Maritime Union of Australia secretary Christy Cain said he was disillusioned and disappointed with WA Labor, but vowed to "box on" over the issue.

WA Maritime Union boss Christy Cain at his headquarters in Fremantle. Credit:Philip Gostelow

"Obviously we haven’t done enough work inside the party, and obviously one should ask what the f--k they, the McGowan Government, are doing," he said.

"We have a platform, which they play lip service to, unless it suits them.