Blackmail charges against two senior CFMEU officials hinge on allegations the union imposed a black ban on Boral, a Melbourne court has been told.
Lawyers for unionists John Setka and Shaun Reardon will cross-examine Boral's chief executive Michael Kane at a two-week hearing in November.
Setka's barrister Robert Richter QC said Mr Kane was an "industrial warrior" and a key figure in what the CFMEU saw as a conspiracy to destroy it.
"He is the warrior who is trying to destroy the CFMEU," Mr Richter told the Melbourne Magistrates Court.
He referenced a recent newspaper article written by Mr Kane and said it was an act of someone "pursuing warfare against the union and it's officials".
Setka and Reardon both appeared in court accused of blackmailing two Boral executives, in an alleged bid to cause a loss to construction giant Grocon.
Documents before the court allege the pair blackmailed Paul Dalton and Peter Head in April 2013.
Mr Richter said the CFMEU denied imposing a black ban on Boral, and the prosecution would rely on that allegation to try to prove the charges against Setka and Reardon.
Mr Kane was the person who asked the Royal Commission into Trade Union Governance and Corruption to investigate alleged blackmail, Mr Richter said.
Prosecutor Ray Gibson had opposed Mr Kane being called to testify.
He said Mr Kane might be a "convenient punching bag", but his evidence was general and wouldn't assist.
Setka and Reardon, secretary and deputy of the Victorian branch respectively, were charged with one count each of blackmail last year and have vowed to fight the allegations.
Speaking outside court, Victorian Trades Hall Council secretary Luke Hilakari said the state's union movement stood strongly with the men.
He said the charges arose out of a politicised "witch hunt" royal commission.
"Every Australian should be concerned that criminal law is being put into our industrial relations system," he told reporters.
Setka and Reardon have been bailed to reappear in court for a contested committal hearing from November 2, where more than 20 witnesses are expected to give evidence.