The Construction, Forestry and Maritime Employees Union has filed a High Court challenge in a bid to overturn its administration.
Former CFMEU national president Jade Ingham confirmed the legal bid was lodged on Tuesday morning.
Prime Minister Anthony Albanese said the government would defend its decision to bring in administrators.
Laws were passed in August to place branches of the embattled union into administration, following reports of corruption and criminal infiltration within parts of the union.
The construction and general division and all of its state and territory branches, including the ACT, were subsequently placed into administration.
Speaking to reporters on Tuesday afternoon, Mr Ingham described the administration laws as an "extraordinary attack" on the CFMEU and other trade unions.
"Whether you like the CFMEU or you hate the CFMEU, this attack should concern anybody in this country that cares about our country and that cares about our democracy," he said.
"That is why we are raising awareness. That is why the High Court challenge has been lodged.
"As I said, it's our belief that these laws are unconstitutional, undemocratic and they are definitely un-Australian."
Mr Ingham said the allegations, first reported by Nine, were about a "handful of people" in the construction union.
"To put things into perspective, there are about 1500 democratically elected workplace delegates and union officials that represent the mighty CFMEU across Australia," he said.
"Allegations were raised about a handful of them and now the entire union has been placed into administration."
The union has launched a crowd-funding campaign dubbed "your union, your choice".
Prime Minister Anthony Albanese said the court action was "fully expected" when asked about it at a press conference on Tuesday.
"Surprise, surprise. John Setka took our entire national executive to court over him being expelled from the Labor Party," he said.
"That's fully expected, and we will stand by our position, and the government's position will be defended."