Taiwan’s telecoms regulator has rejected a proposal to merge Asia Pacific Telecom (APT) and Ambit Microsystems because the firms failed to provide details on a strategic alliance with Taiwan Mobile.

The rejection comes just a week after the country’s National Communications Commission (NCC) said it was investigating complaints by three rivals of APT and Taiwan Mobile that the two operators’ 4G roaming agreement is illegal.

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

The NCC approved APT’s 4G licence in late October, giving it six months to offer 4G service. APT is the country’s fifth 4G player and said in October it planned to launch 4G service last year in the 700MHz band. But it has emerged that it is sharing Taiwan Mobile’s network and offering lower rates than Taiwan Mobile, which also has drawn complaints from the public and the attention of the regulation for possible fair trade violations.

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.

Ambit, a unit of Hon Hai Precision (better know as Foxconn), brought a 15 per cent interest in APT in May. It said it will submit a new application, the China Post said.

Taiwan Mobile is locked in a battle for second place with Far EasTone – they both have about 7.4 million connections and just under a 23 per cent market share, according to GSMA Intelligence. Market leader Chunghwa has a 33 per cent share and 10.8 million connections. APT has 2.9 million connections and a 9 per cent share.