The Fair Trade Commission is expected to open criminal investigations into 11 major water-treatment plant makers that were raided by the antitrust watchdog in August for allegedly rigging local government bids, sources said Saturday.

The companies participated in tenders between January and March 2005, the sources said.

The companies are Ebara Corp., Kurita Water Industries Ltd., Nishihara Environment Technology Inc., JFE Engineering Corp., Sumitomo Heavy Industries Ltd., Mitsui Engineering and Shipbuilding Co., Mitsubishi Heavy Industries Ltd., Kubota Corp., Hitachi Zosen Corp, Ataka Construction & Engineering Co. and Takuma Co.