South Korea's antitrust watchdog on Thursday fined 21 construction companies a combined 132.2 billion won ($125.9 million) for collusion in the bidding process for a large-scale subway construction project.

Those subject to the fine include big name builders such as Hyundai E&C, Hyundai Development Company, POSCO E&C, GS E&C, SK E&C and Daewoo E&C, according to the Fair Trade Commission.

The FTC said it will refer 15 of the companies to the prosecution for further investigation.

The builders allegedly secretly held meetings and exchanged opinions in advance to determine who should be selected to lead the project for almost entire sections of the 2.16-trillion-won subway line. The bidding was held in 2009.

Those who were not chosen still participated in the bidding competition perfunctorily to help others win the final bidding by submitting low-quality construction designs, the watchdog said.

Daewoo E&C was fined the largest 16 billion won. Hyundai E&C came next with 14.1 billion won, followed by Hyundai Development Company with 14 billion won and SK E&C with 12.8 billion won, the FTC said.

GS E&C and POSCO E&C were fined 12 billion won and 9.6 billion won, respectively. POSCO E&C was also ordered to pay 145 million won for obstructing the FTC's on-spot investigation by removing computer hard drives and deleting related data. (Yonhap News)