One of the CFMEU’s biggest power bases is under threat from a dramatic plunge in membership since the union was forced into administration, despite efforts by the new regime to stem an exodus nationally.

Leaked figures, seen by The Australian Financial Review, show membership in CFMEU NSW – the union’s second-biggest branch – has declined by almost 17 per cent in the year to March, from almost 18,000 members to 14,900, while South Australia has fallen by 16 per cent to just 2000 members.