Ms McManus told the ABC's 7.30 on Wednesday night she believed in the rule of law "where the law's fair, where the law's right, but when it's unjust I don't think there's a problem with breaking it".

Union leaders rallied behind Ms McManus' defence of breaking the law where it was "unjust" but Opposition Leader Bill Shorten swiftly distanced himself from the comments.

"If you don't like a law, if you think a law is unjust, use the democratic process to get it changed," he said.

"I just don't agree. We believe in changing bad laws not breaking them."

Victoria's Labor Premier Daniel Andrews agreed, saying Australia's democratic system was based on people campaigning to change unjust laws.

"I don't agree that you can pick and choose which bits of the law that you follow and I would respectfully submit I think most Australians are probably with me on that," he said.

Prime Minister Malcolm Turnbull said the remarks betrayed the true nature of the labour movement while Employment Minister Michaelia Cash said the comments were "outrageous".

Environment and Energy Minister Josh Frydenberg said the royal commission into trade union corruption had shown laws were broken on building sites.

"I have no sympathy with the idea that you should break the law of the land in order to pursue your political objectives here," he said.

Defence Industry Minister Christopher Pyne dismissed the call as "anarcho-Marxist claptrap".

Business Council of Australia chief executive Jennifer Westacott said Ms McManus had been "grossly irresponsible" for making statements that could have "dangerous real-world consequences, signalling to individuals around the country that it's OK to take the law into their own hands".

"What kind of society will we have if everyone can simply choose to ignore any laws they don't like?," she said

Ms McManus's comment was in response to a question about whether the ACTU should distance itself from the Construction, Forestry, Mining and Energy Union which is facing more than 100 separate court proceedings including criminal blackmail charges over a dispute with Boral in Victoria.

Ms McManus stood by her controversial comments on Thursday. She said Australia was built by "working people who have had the courage to stand up to unfair and unjust rules and demand something better".

"Every single Australian benefits from superannuation, Medicare, the weekend and minimum wages - these were all won by our parents, grandparents and great-grandparents taking non-violent so-called illegal industrial action," she said.

Prominent unionists also lined up to support Ms McManus, putting themselves at odds with Mr Shorten's repudiation.

National Secretary of the Transport Workers Union Tony Sheldon said employers have been gaming the industrial relations system and laws needed to change to protect workers' wages and conditions.

"Sally is saying the obvious about what needs to be done in trying to deal with a system that is broken," he said.

"We need to do whatever it takes."

Tim Ayers, NSW Secretary of the Australian Manufacturing Workers Union, said Ms McManus' plain speaking was welcome.

"She isn't a politician and she isn't the type to fall for the shallow 'gotcha' journalism," he said.

"It's just common sense that unions undertake industrial action - that is what a democratic society looks like."

CFMEU assistant secretary Dave Noonan said Australia has some of the narrowest laws around industrial action in the OECD.

"Sally McManus has got absolute support from the trade union movement. I don't think you will find any affiliated union that has significant differences with what she said."

The deputy chair of the NSW ALP industrial relations policy committee, Anthony D'Adam, said unions needed to defend the right to strike as a basic human right.

"Sally is just articulating a long-held position of the union movement which is that the right to strike is sacrosanct and laws that effectively take away that right are unjust and shouldn't be complied with," he said.

Labor Party elder and historian, Rodney Cavalier, a former NSW Minister, said it was governments' role to enforce the law - or repeal it, if unjust.

He said civil disobedience was based on respect for the rule of law.

"The disobedient understand that the law must be enforced and are prepared to take the consequences, including forfeiting their freedom to serve a custodial sentence. Punishment-free martyrdom is not an option for those openly disobedient," he said.

"There is a corresponding obligation on government to enforce the law or repeal it.

"The governments of Chifley and Hawke did not hesitate to take whatever action was required to deal with any person or institution operating outside the law.

"I am sure the leaders of the Shorten Government will be making it expressly clear that they will be enforcing the law in any and all circumstances."

Assistant Industry Minister Craig Laundy said Ms McManus' comments showed why the reinstatement of the Australian Building and Construction Commission was necessary.

"Only a union movement could quite clearly promote an anarchist to its key position and I just hope she keeps finding a camera every day and telling us what she thinks," he told Sky News.

With Rania Spooner