Taiwan's Asia Pacific Telecom and Taiwan Mobile have been fined TW$300,000 ($9,500) each for allegedly violating requirements to report on a 4G roaming agreement.
The companies signed a 4G roaming pact on September 25 but did not file a report to regulators detailing the agreement until December 17, Digitimesreported, citing the National Communications Commission (NCC).
Rival operators Chunghwa Telecom, Far EasTone and Taiwan Star petitioned the NCC to investigate the pact in January.
Sources told Digitimes that the regulator is also investigating whether the agreement violates Taiwan's Telecommunications Act and Fair Trade Act, and probing whether it represents efficient utilization of frequency band units.
The co-operation was motivated by plans for APT to provide 4G services over established operators' base stations.
But the agreement allows APT to charge lower monthly prices for services than Taiwan Mobile does to its own customers. Rival operators also oppose the deal on the grounds that it allows APT to provide 4G services without sufficient efforts to build its own infrastructure.