Boral filed contempt proceedings in the Victorian Supreme Court against the Construction, Forestry, Mining and Energy Union (CFMEU) last month.

Boral alleges a CFMEU blockade stopped it supplying concrete to the Regional Rail Link site in May last year, also disobeying a court order that prevented the union doing this.

Attorney-General Robert Clark’s office made an application to become a party to the proceedings, stating it wanted to do this rather than issue a separate proceeding.

Justice John Digby ruled the attorney-general established “sufficient interest” in the proceedings to become a party.

He said the alleged contempt might have an element of “public defiance” in the failure to comply with a court order, and the context of the case was important because the CFMEU was one of the most significant unions in Australia.

Justice Digby adjourned proceedings for a date to be fixed.