Korea’s Fair Trade Commission said Monday that it has imposed penalties against KCC and Hankuk Glass Industries after detecting that the two flat-glass manufacturing giants colluded to rig prices of their building materials.

The antitrust agency will slap combined fines of 38.4 billion won ($34.1 million) on the two companies, and name one executive from each company involved in price collusion to be prosecuted.

Its penalty measures also include forbidding the two manufacturers to share any inside market information from now on, the FTC said.

KCC will need to pay 22.4 billion won and Hankuk Glass Industries about 16 billion won to the regulator.

KCC is Korea’s leading construction materials maker, owned by chairman and CEO Chung Mong-jin and his family. Chung is the nephew of the late Hyundai Group founder Chung Ju-young.

Hankuk Glass Industries is a foreign-invested company whose majority shareholder is SOFIAG, an investment unit of France-based Saint-Gobain S.A., a global building-glass maker with operations in 64 countries, according to a regulatory filing.

The two listed companies have been dominating Korea’s construction glass materials market with more than 80 percent market share over the last 20 years, the antitrust agency noted.

Hankuk Glass Industries, established in 1957, solely led the market until KCC entered the flat-glass arena in 1988 and started competing with the foreign-invested company.

The FTC said fierce market competition led them to collude and raise prices of transparent flat glasses four times by 10 to 15 percent between 2006 and 2009.

The two executives to be prosecuted, from their respective companies’ sales divisions, met in person or talked on their mobile phones before rigging the prices of their glass materials, the FTC said.

KCC shares closed at 336,500 won, up 10,500 won or 3.22 percent on Monday despite being levied with fines. Hankuk Glass Industries saw its stock price drop 500 won, or 2.63 percent, to 18,500 won.

By Park Hyong-ki (hkp@heraldcorp.com)