South Korea's antitrust watchdog said Monday that it has levied a combined 37.1 billion won ($33.2 million) in fines on three foreign auto parts firms for allegedly rigging bids.

Denso Korea Automotive Corp., an auto parts supplying unit of Japan's Toyota Motor Corp., and Hyundam Industrial Co. owned by Japan's Aisan Industry Co. had been accused of colluding to participate in bids for engine fuel pumps arranged by South Korean carmakers from August 2007 to February 2009, according to the Fair Trade Commission.

Denso Korea and Delphi Powertrain Systems Korea Co., a local unit of US Delphi Automotive, are also under suspicion for joining forces in separate tenders for a variable valve timing system between 2009 and 2012.