The unions here are fiercely pro left (ALP). They splash a huge amount of cash in direct donations and indirectly via media PR. Ain't no way that comes from a special volunteer-only donor "fund".
The CFMEU (Construction, Forestry, Mining, Energy Union) in particular donates to and publicly supports the left. The irony of supporting the very people trying to shut down their industry in an attempt to pacify the greens that they rely on to stay in power seems to escape the rank and file of the union.
Also a large number of elected persons from said party are former or current union officials. Never done a days work in their life. Union "official" then career politician.