The mining union’s bid to split from the CFMEU over a fallout with controversial unionist John Setka has been thrown into disarray after the workplace tribunal found the law does not permit it to divorce the militant union.

The Fair Work Commission on Tuesday rejected the mining union’s application to ballot its members on withdrawing from the Construction, Forestry, Maritime, Mining and Energy Union after finding parts of the Morrison government’s legislative changes, introduced specifically to enable the divorce, did not apply to the union.