Australia’s competition watchdog is investigating whether the NSW government has done a deal that could prevent the expansion of Newcastle’s port, telling stakeholders it’s “concerned” about current arrangements.

In a letter to industry figures, seen by AAP, the ACCC says it “has concerns about arrangements that may limit or prevent the development of a container terminal at the Port of Newcastle”.

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.

Labor says the NSW government and then treasurer Mike Baird struck a deal in 2012 with the private consortium NSW Ports when selling the Kembla and Botany leases.

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 watchdog’s letter, dated March 28, says the ACCC is investigating whether any competition issues arise under the Competition and Consumer Act.

It notes the act prevents contracts, arrangements or understandings which have the purpose or effect of substantially lessening competition.

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 says the reported deal was “clearly anti-competitive and designed to entrench a private monopoly”.

“It is astonishing that any government would enter into a secret deal so deliberately designed to hurt Newcastle’s economic development,” the Labor leader said in a statement.

The government and NSW Ports have been contacted for comment.

-AAP