The nation’s antitrust watchdog said Sunday it had fined Samsung C&T and Hyundai Development Co., two of Korea’s top 10 builders, a combined 19 billion won ($17.7 million) for colluding in 2009 to fix the bidding price for the third stage of a construction project to build Seoul subway Line No. 9.

The Fair Trade Commission slapped the construction arm of Samsung Group with a fine of 16.2 billion won, while Hyundai Development was fined with 2.7 billion. The watchdog added it would report irregularities by the two builders to the prosecution.

According to the authorities, the two builders colluded to keep the bidding price high to increase profits.

Samsung won the deal, writing down 94.1 percent of the expected 199.8 billion won bidding price. Hyundai lost the deal with a 94 percent bid.

“The reason why the two builders wrote down 94 percent is because both knew that the rate was the highest bid for maximum profit without getting caught,” said Shin Young-ho, an FTC official.

The watchdog tends to crack down on companies that bid more than 95 percent of the expected price on both cartel and price-rigging suspicions.

Samsung C&T’s project to build the 1.56-kilometer-long subway Line No. 9, which stretches from Jamsil Hospital in Samjeon-dong of southern Seoul to Seokchon Station in Seokchon-dong, received media attention in August when an 8-meter-long, 2.5-meter-wide and 5-meter-deep sinkhole was found near the construction site.

After a site inspection, the Seoul Metropolitan Government concluded that subway construction under the road by Samsung C&T caused the sinkhole. Samsung’s construction arm vowed to restore the sinkhole with grave responsibility.

The FTC said it was looking into possible additional price rigging cases in other construction sections of Line No. 9.

By Bae Ji-sook (baejisook@heraldcorp.com)