KDDI, Softbank and Rakuten were among 28 companies to lodge a formal complaint against attempts by state-backed NTT to take listed subsidiary NTT Docomo private, claiming it would damage competition and development in the market.

In a joint letter to Japan’s Minister of Internal Affairs and Communications Ryota Takeda, major rivals outlined a scathing assessment of the proposal announced by NTT in September and its impact on the dynamics of the mobile industry.

The parties noted if NTT Docomo became a wholly-owned subsidiary of its largest shareholder NTT, the cohesion between the two would be further strengthened.

“As a result, strong market power will be created, competitors will be eliminated, fair competition in the telecommunications market will be hindered, and user profits generated through competition will be impaired.”

Measures proposed by the allied businesses include a public consultation into the issue to allow the whole ecosystem and independent experts to offer their assessments; or (should the deal go ahead) enforceable rules to be put in place to retain fair competition.

“Given the impact on competition, it is necessary to re-discuss the fair competition requirements necessary for moving toward 5G and beyond 5G,” the group added.

Aside from direct mobile rivals, other companies to sign the complaint include Japan Cable and Telecommunications Association, Colt Technology, MVNO Line Mobile and Okinawa Cellular Telephone Co.

The group of 28 stated they also have the support of a further nine companies dealing in, or related to, the telecoms market in the country on their stance against the move.