The powerful Construction Forestry Maritime Mining and Energy Union is set to lose a large chunk of its membership after a decisive ballot.
Mining and energy division members voted 98 per cent in favour of splitting from the CFMMEU and forming the independent Mining and Energy Union.
General president Tony Maher said the results clearly confirmed the will of mining and energy division members.
"We pursued this path because members told us they no longer felt at home in the CFMMEU," Mr Maher said in a statement on Thursday.
"Our members want a union that focuses on the considerable needs and challenges of mining and energy workers; while also working constructively and collaboratively within the broader trade union movement."
General secretary Grahame Kelly said the ballot had been logistically complex but managed with "efficiency and professionalism".
The division will now apply to the Federal Court seeking orders to fix a withdrawal date.
The court application may be made after 30 days from the declaration of the ballot results.
Divisions of the CFMMEU have been in and out of court in recent years arguing over member poaching.
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