The charges against CFMEU Victorian leader John Setka and his deputy Shaun Reardon were withdrawn on Wednesday, mid-way through a hearing in Melbourne Magistrates Court.

It was alleged they blackmailed Boral managers Paul Dalton and Peter Head at a coffee shop meeting in Melbourne in April 2013.

ACTU secretary Sally McManus said she was concerned former prime minister Tony Abbott and his then employment minister Eric Abetz were involved in the events which led to the court action.

"At what levels were the government involved in what we believe were trumped up charges against these union leaders?" Ms McManus told Sky News on Thursday.

But Senator Abetz dismissed the claim as laughable.

"The first my then ministerial office became aware of such allegations was when issues were placed on the public record in the Heydon royal commission," he said in a statement.

Setka and Reardon were charged in 2015 after a joint Victorian and federal police unit investigation, following a referral by the trade union royal commission.

It was alleged the pair threatened to blockade Boral plants and trucks if the company refused to meet union demands.

Ms McManus said the two men had stood up for safety in an extremely dangerous industry.

But Jobs Minister Michaelia Cash said Setka had proudly broken the law in the past, before denying the dropped charges were embarrassing for the government.

Setka admitted to having a small rap sheet from growing up in Footscray, a working-class suburb in Melbourne's west, but defended his actions as a union official.

"We get fantastic pay rises and good conditions for our members because we fight it outside the law," he told Sky News.

Prime Minister Malcolm Turnbull said unionists did not have privilege to break the law without consequences.

Opposition Leader Bill Shorten said he wouldn't protect anyone from breaking the law, but the prosecution dropping charges against the CFMEU pair spoke for itself.

Outside court on Wednesday, Setka said there was evidence of talks involving Boral, Mr Abbott and former Victorian premier Denis Napthine.

"It was just a conspiracy, all the way through."

Australian Associated Press