The agency known as the KPPU said in a statement late on Wednesday the companies, which included subsidiaries of some of the country's biggest conglomerates, were suspected of price fixing and controlling supply of cooking oil.
Wilmar, Musim Mas and Sinar Mas said they would cooperate with the investigation. Salim Ivomas did not immediately respond to Reuters' requests for comment. In an attempt to control domestic prices, Indonesia restricted exports of palm oil which is used for cooking oil, and earlier this year put a limit on maximum retail prices for branded cooking oil, which led to scarcity in the market.