The head of the Construction, Forestry, Maritime, Mining and Energy Union will step down after a damaging internal split within the union and a fallout with John Setka.

CFMEU national secretary Michael O'Connor tendered his resignation on Thursday after saying the union was falling apart due to "irreconcilable differences" and accusing elements of the union of "failing the test of political maturity", which would have entailed compromising and working together.