Investigators from the Fair Trade Commission searched about 40 offices of more than 20 machinery makers Tuesday over suspicions that they rigged bids on contracts for public floodgate projects.

Among the companies raided were Mitsui Engineering & Shipbuilding Co., Mitsubishi Heavy Industries Ltd., Ishikawajima-Harima Heavy Industries Co., Sumitomo Heavy Industries Ltd., JFE Engineering Corp., Komai Tekko Inc., Takada Kiko Co. and Hitachi Zosen Corp.

The Tokyo head office of the Japan Association of Dam & Weir Equipment Engineering, a floodgate makers' group, was also searched.

The public works projects under suspicion were financed by the central and local governments as well as the state-backed Japan Water Agency.

Mitsui Engineering, Mitsubishi Heavy, Hitachi Zosen, Sumitomo Heavy, Kawasaki Heavy and JFE Engineering were contacted for comment on the raids, but would only confirm their offices had been searched.

The companies are suspected of rigging bids to keep order prices high and to divide up the contracts among them.

Bid-rigging is illegal under the Antimonopoly Law and violations can net up to three years in prison or a fine of up to 5 million yen.

A large floodgate project in Japan costs billions of, yen with the market estimated to be worth between 60 billion yen and 70 billion yen annually.