Auckland Council chief executive Doug McKay has become a non-executive director of the Bank of Zealand - a company with business links to the council.
Mr McKay and Mayor Len Brown's office say any potential conflict of interest is managed in accordance with council policy.
The chief executive review subcommittee, chaired by Mr Brown, gave Mr McKay approval last year to accept a board appointment before he leaves the council in December.
The BNZ has a number of commercial arrangements with the council, including providing over-the-counter payment services for rates and water bills and being involved in the council's overseas borrowing programme.