West Australian Premier Mark McGowan has declared he won't be silenced after his bitter feud with Clive Palmer escalated to defamation proceedings.
The billionaire mining magnate has filed paperwork in the NSW registry of the Federal Court alleging Mr McGowan had defamed him.
It is not yet clear what the case refers to.
It comes as Mr Palmer seeks almost $30 billion in damages over a decision by the former government not to assess one of his mining projects.
The premier says Mr Palmer's legal action does not daunt him.
"I was elected as premier ... to ensure that I leave the state in a better position than I found it. Mr Palmer is a threat to that, so I'll continue to fight," he said on Friday.
"I won't be silenced, I won't be stopped, by him issuing these legal proceedings."
Mr Palmer on Friday launched yet another legal claim against WA, this time accusing the government of "unconscionable conduct".
He said his company Mineralogy had commenced fresh proceedings in the Federal Court and would seek to amend its claim against the state to reflect additional damages it had suffered.
"The amount of damages is likely to exceed the damages claimed in the arbitration the state had previously agreed to but legislated to terminate,'" Mr Palmer said in a statement.
"Under their unconstitutional Act, we cannot take a dispute to any court. The simple fact is the state of Western Australia does not have the power to control either the Federal or the High Court of Australia."
WA's parliament last week passed extraordinary legislation to amend a 2002 state agreement with Mr Palmer's Mineralogy company and terminate arbitration between the two parties.
The bill is designed to block Mr Palmer from claiming damages from the state.
Mr Palmer secured orders in the Queensland Supreme Court to have the arbitration awards formally registered shortly before the bill was signed into law.
He claimed this meant WA's "draconian and disgraceful" legislation would now be invalid under the constitution.
The matter returned to the Supreme Court on Wednesday with the WA government arguing the orders should be set aside.
Justice Glenn Martin adjourned the hearing until September 10.
Mr Palmer, through Mineralogy and International Minerals, is pursuing damages over a 2012 decision by the former Liberal government not to assess his proposed Balmoral South iron ore mine in the Pilbara.
The billionaire mining magnate is separately challenging WA's hard border closures in the High Court.
But he offered to withdraw the case earlier this year if officials agreed to move the unrelated arbitration hearings from Perth to Canberra.
Australian Associated Press