A union picket at Fremantle Port is preventing ships from unloading farm machinery in the middle of the state’s bumper harvest in what industry sources claim is part of an unlawful secondary boycott.

A group of unionists has gathered for the past two days at one of the entrances to the Fremantle terminal for Qube-rival Linx and the company’s wharfies are not crossing the line to service ships owned by Qube’s largest customer Wallenius Wilhelmsen.