NSW Treasurer Dominic Perrottet is not concerned the competition watchdog is investigating whether his government has done a deal that could prevent the expansion of Newcastle's port.
The ACCC is concerned arrangements may "limit or prevent" the development of a container terminal at the Port of Newcastle.
In a letter to industry figures, seen by AAP, the ACCC states it's investigating whether any competition issues arise under the Competition and Consumer Act.
The cited "arrangements" could refer to the controversial sale of the Port Botany and Port Kembla leases and "secret deals" between the government and the private operator, according to the state opposition.
The deal reportedly means the Port of Newcastle, if it were to expand, would have to pay a fee to NSW Ports as compensation for their loss of container shipping business.
The treasurer's office in a statement on Wednesday said it wasn't concerned about the ACCC's investigation and the government would assist the watchdog "in whatever way they require".
A spokesman told AAP that Treasury stood by the controversial decision to privatise the ports.
"Funds from the (Newcastle) lease have been used to help the government invest in its once-in-a-generation infrastructure program," he said.
Asked if the government would welcome an expansion of Newcastle the spokesman said: "Any decision to expand the container capacity ... is a matter for the operator of the Port of Newcastle."
The ACCC has told AAP it is investigating contractual restrictions which could prevent the expansion of container throughput at "certain ports".
"Specifically, we'd like to understand whether these restrictions may limit competition in a way that means customers exporting commodities, such as cotton and grain producers, are faced with less competitive prices and fewer options for doing so," an ACCC spokesman said in a statement.
Opposition Leader Luke Foley earlier this week said the reported deal was "clearly anti-competitive and designed to entrench a private monopoly".
NSW Ports - which operates Port Botany and Port Kembla - has been contacted for comment.
