The construction industry watchdog has launched legal action against the Queensland head of the plumbers' union for allegedly coercing a subcontractor to kick out its project manager.

Communications Electrical and Plumbing Union Queensland secretary Gary O'Halloran, an organiser and 25 workers face fines of up to $42,000 as part of the Australian Building and Construction's case over an unlawful stoppage at the $590 million Southpoint hotel and luxury apartment development site in 2017.