Softbank BB Corp. sought a court injunction Wednesday against a government plan to reallocate frequencies within the 800-megahertz band to two leading mobile phone operators.

Softbank BB President Masayoshi Son, the head of the Softbank Corp. group., said the injunction was filed with the Tokyo District Court against the Internal Affairs and Communications Ministry. It is the first time legal action has been taken concerning the allocation of radio waves.

Softbank is the operator of the Yahoo BB high-speed Internet access service.

Frequencies within the 800-MHz band are said to be suitable for mobile phone services because they pass through buildings and other barriers more readily than other frequencies.

To improve the efficiency of radio waves, the ministry plans to sort out frequencies used by existing mobile phone operators and reallocate those within the 800-MHz zone primarily to NTT DoCoMo Inc. and KDDI Corp. This effectively excludes newcomers such as Softbank BB.

The ministry plans to allocate other frequencies, such as those in the 1.7- and 2-gigahertz bands, to other cell-phone operators, including new carriers.

Softbank BB, which intends to enter the cell-phone service market, said the ministry plan is unfair and has called for frequencies within the 800-MHz band to be allocated to other cell-phone operators as well.