A property developer and Liberal politician on Sydney's most controversial council made millions building and selling apartments that allegedly breach their development approval.

Auburn City Council staff have known for years that there were "irregularities" with a unit block developed by councillor Ronney Oueik, the Liberal Party's candidate for the seat of Auburn at last year's election.

But the council is only now pursuing legal action against Cr Oueik, a political ally of Salim Mehajer, following repeated inquiries by Fairfax Media over the past month regarding one of his apartment developments in Auburn.

The 41-unit complex at 40-46 Station Road was approved in 2001 to contain 12 three-bedroom units and 29 two bedroom units.