The Fair Trade Commission has questioned Tokyo Electric Power Co. officials over possible violation of the Antimonopoly Law in connection with an upcoming bid to select a power supplier for a government building, industry sources said Saturday.

The antitrust watchdog suspects Tepco, the nation's largest power company, offered an unfair power supply deal to Tokyo Gas Co. vying for the power supply contract, the sources said. Tokyo Gas is not able to fully supply electricity on its own and must purchase some from Tepco.

Normally, Tepco allows clients to choose between two options in buying power from the company -- one package has a nightly discounted rate and a high daytime rate. The other has a high nightly rate and a discounted daytime rate.