The building industry watchdog is extending its reach to the waterfront for the first time, threatening to impose higher fines and strict laws to curb the power of the militant maritime union and prevent disruption on the supply chain.

Australian Building and Construction Commission inspectors are investigating an allegedly unlawful picket at Fremantle Port that forced ships to divert urgent cargo to the east coast last year because of the Maritime Union of Australia’s three-month industrial campaign against stevedore Qube.