Militant unionist Christy Cain is set to become the new leader of the powerful CFMEU despite a last-minute bid from the mining division to stop the coronation and a warning from the manufacturing arm that his election could trigger its exit from the union.

The Construction, Forestry, Maritime, Mining and Energy Union will hold a national executive meeting on Friday to vote on the maritime union official as its national secretary after changing union rules to allow his election, but in a way that the mining division claims gives construction “absolute and unfettered control” of the CFMEU.