Blackmail charges against the leaders of Victoria's biggest building union might never get to trial even if the two accused men lose their next court challenge.

Construction, Forestry, Mining and Energy Union state secretary John Setka and deputy Shaun Reardon are trying to have the charges against them quashed and will take their fight to the Court of Appeal next year, having already had a magistrate and a Supreme Court judge rule against them and declare the charges legitimate.

CFMEU leaders John Setka (left) and Shaun Reardon allegedly blackmailed Boral executives. Credit:Justin McManus

With the case close to entering its third year before the courts, Mr Setka and Mr Reardon on Tuesday appeared before Melbourne Magistrates Court, which heard the two men and their lawyers would take their fight against the validity of the charges to the High Court if the Court of Appeal ruled against them.

If the matter goes to the High Court, there is a chance Victoria's Director of Public Prosecutions might decide the case is not worth prosecuting, the court heard.