The prudential regulator repeatedly warned Cbus that it had failed to fix major governance issues and will now investigate payments made by the $100 billion industry superannuation fund to its union backers.

Concerns raised by the Australian Prudential Regulation Authority about how Cbus managed risks and ensured it was making decisions in the best financial interest of its members stretch back four years, according to documents published by the regulator after the superannuation fund chaired by former treasurer Wayne Swan agreed to lift its standards.