India’s antitrust regulator has ordered a probe into alleged anti-competitive practices by Denmark’s A.P. Moller-Maersk and Dubai’s DP World at the terminals they operate at the country’s largest container port in Mumbai.

The decision by the Competition Commission of India (CCI) to investigate follows a complaint by Singapore’s PSA International Pte Ltd, which alleged that Maersk and DP World created entry barriers to hinder the growth of PSA’s terminal by colluding on certain charges they levy at the state-owned Jawaharlal Nehru Port Trust (JNPT).

Handling 66 million tonnes of cargo in the last fiscal year to March, JNPT is critical to India’s international trade. The port handles more than half of India’s traffic of shipping containers each year.

Units of Maersk, DP World and PSA operate four of the port’s five terminals, with the fifth owned by the government. The PSA terminal, inaugurated by Prime Minister Narendra Modi in February, is planned to be the largest, expected to nearly double JNPT’s capacity and help fulfill the government’s vision of boosting India’s economic growth by modernizing its ports.

According to reuters.com¸the dispute centers around so-called inter-terminal transfers.