Taiwan’s telecoms regulator is investigating complaints by three rivals of Asia-Pacific Telecom (APT) and Taiwan Mobile that the two operators’ 4G roaming agreement is illegal.

The National Communications Commission (NCC) said it will hold hearings to determine if the partnership complies with the country’s telecoms act, the Taipei Times said.

Chunghwa Telecom, Far EasTone Telecommunications and Taiwan Star Telecom complained that APT, which has a 4G licence, is using Taiwan Mobile’s network and has not built its own 4G network.

The Times reported that Taiwan Mobile has claimed that the partnership merely allows APT’s customers to connect to its service in areas where APT doesn’t yet have coverage.

In addition to network sharing, the NCC will also look into whether the lower rates charged by APT, using Taiwan Mobile’s 4G network, violate fair trade laws.

In early January, the NCC ruled that Taiwan Mobile customers, who pay 36 per cent, or TWD501 ($15), more for 4G service than APT’s 4G customers must fulfill the terms of their contracts and pay any penalties if they want out.

The NCC said that while the telecoms law allows roaming agreements, it doesn’t mean any type of roaming partnership is allowed, the Times said. The two companies’ business plans state the number of base stations to be rolled out over the next two years. If these targets aren’t met, the NCC can impose fines.