First Union wants lump-sum payments offered to Auckland bus drivers to be investigated by the auditor-general.
Union secretary Karl Anderson said the privately run Howick and Eastern Buses had offered drivers payments in exchange for forgoing overtime and weekend rates.
That was a misuse of public funds, he said. The money was for public transport services and should not be used as an inducement for drivers to cut their wages.
Mr Anderson asked the auditor-general to investigate whether Auckland Transport was aware how the private bus companies were using council funding.
The company also wanted drivers to sign an individual agreement in exchange for the money, Mr Anderson said.
Auckland Transport declined to comment, and said it was a matter between the company and its staff.
Howick and Eastern Buses have not responded to an RNZ News request for comment.