The Fair Trade Commission ordered three steel sheet makers Thursday to cease their illegal cartel and imposed a record ¥15.5 billion in combined penalties for their alleged price-fixing.

The three are Nippon Steel & Sumikin Coated Sheet Corp., Nisshin Steel Co. and Yodogawa Steel Works Ltd. The amount of penalty surcharge imposed on the three is the highest in price-fixing cases, topping the ¥12.9 billion slapped on 44 bridge builders in 2006 over their alleged bid-rigging practices.

Tokyo-based Nippon Steel & Sumikin was ordered to pay about a ¥6.34 billion surcharge, Nisshin Steel, also based in Tokyo, about ¥5.49 billion and Osaka-headquartered Yodogawa Steel some ¥3.68 billion.

Nippon Steel & Sumikin declined comment on the commission's order, while Nisshin Steel and Yodogawa Steel said they will examine the order before taking any action.

Another steel sheet maker, JFE Galvanizing & Coating Co., was also a party to the price cartel agreements. But the company was not slapped with a surcharge because it voluntarily reported the price-fixing cartel to the FTC.