A senior Japanese official has called for new regulations to prevent NTT, the world’s biggest listed telecommunications company, from abusing its dominant position in the domestic market as it prepares to offer joint fixed-line and mobile services.

Yasu Taniwaki, director of competition policy at the telecommunications ministry, said a “new framework” was needed simply “to keep up” with NTT’s decision to announce fixed-mobile services, while the ministry planned to “investigate whether the merging of the [fixed-line and mobile] markets is going to cause dominance” by NTT.

NTT wants to offer customers the option of a single phone number that would operate from fixed-line infrastructure when they are at home and via mobile services when they are out.

The company recently won permission from the government to offer fixed-mobile services. It is seen as having an immense advantage in the market for such services because its NTT East and West subsidiaries control about 90 per cent of the fixed-line market. Its NTT DoCoMo mobile arm has 60 per cent of the wireless market.

Mr Taniwaki said regulators were examining whether NTT companies would have to be given “specific permission” for individual fixed-mobile services. That reflects the delicate game Japanese regulators have to play as they try to allow NTT to offer innovative services while preventing it from monopolising the market.