The Fair Trade Commission filed a complaint with the prosecutor general Thursday against Kubota Corp. and two other water- and gas-pipe makers for allegedly arranging a cartel to fix their market shares, officials said.

According to the FTC, Kubota conspired with Kurimoto, Ltd. and Nippon Chutetsukan K.K. to restrict market competition by prearranging a division of orders from local governments for straight ductile cast iron pipes between fiscal 1996 and 1997.

The FTC started investigating the case in May after a Kanagawa-based ombudsman alleged that the three firms were rigging bids. The three firms have monopolized the market, which totals about 115 billion yen, with Kubota taking a 60 percent share, Kurimoto 30 percent and Nippon Chutetsukan 10 percent, according to sources close to the FTC.

Annual output of ductile cast iron pipes has been around 600,000 tons in recent years. "The nature of this incident is vicious," said Kyohei Sakai, a FTC official in charge of inspection. "It greatly affects people's lives as their business involves distribution of water."

Tokyo district public prosecutors will investigate, and the FTC is expected to order the three firms to abandon the business practices in question. Kubota declined comment on the case.