A High Court challenge has been launched after the construction union was placed into administration, with the commonwealth accused of "active treachery".
But Prime Minister Anthony Albanese was not surprised by the CFMEU legal move, saying the federal government's position would be defended.
Former CFMEU national president Jade Ingham confirmed the High Court challenge had been filed on Tuesday, accusing the federal government of union bashing.
"It's our belief that these laws are unconstitutional, undemocratic and they are definitely un-Australian," he said in Brisbane.
"Any political party that's engaged in union bashing over the years never survives.
"It's not a very smart political play. It's never worked for the conservatives and I'm really, really surprised that the Labor Party thought that it would work for them."
Attorney-General Mark Dreyfus placed the union's construction and general division into administration on August 23, alongside all of its state and territory branches.
Laws giving the relevant minister powers to intervene and slap life bans on CFMEU officials also passed the parliament in August.
The government's move followed allegations of corruption and bikie infiltration within the CFMEU.
The union had signalled it would start a court challenge, saying members were denied due process and their democratic rights.
More than a week after Mark Irving KC was unveiled as the CFMEU's administrator, the High Court challenge was confirmed.
"The most important people in this are the members of the CFMEU whose voices have been excluded," Mr Ingham said in a statement.
"Members are furious ... their union has been stolen from them.
"This is active treachery and class warfare against the working class in this country from the state and federal governments."
After the attorney-general placed the construction union into administration, more than 200 elected CFMEU officials were immediately terminated.
The administration period could last up to five years.
"This is an extraordinary attack, one that most in the union movement wouldn't have expected from a party that has done nothing but benefit from the efforts of our union and of our members," Mr Ingham said.
"They understand that this is not just about the CFMEU, that this is a very dangerous precedent to be set.
"And what the Labor Party have done is given a blueprint to the conservatives of this country to attack trade unions."
Union bosses across the country vowed to fight the administration when tens of thousands marched throughout the nation last week, branding the Labor government a traitor to the labour movement.
Up to 50,000 workers attended a rally in Melbourne and thousands more went out in Sydney, Brisbane and other regional capitals, ignoring threats their pay could be docked by taking the unprotected action.
Workplace Relations Minister Murray Watt, who oversaw the passing of the laws allowing for administration, last week said they were written to withstand a legal challenge.
Mr Albanese also backed them after hearing of the High Court challenge.
"Surprise, surprise. (Former Victorian secretary) John Setka took our entire national executive to court over him being expelled from the Labor Party," he told reporters on Tuesday.
"That (High Court challenge) is fully expected. We will stand by our position and the government's position will be defended."
Mr Ingham said a crowdfunding campaign had been launched to support the High Court battle.
