The Fair Trade Commission on Wednesday launched an investigation into five construction companies on allegations that they colluded in a controversial project to refurbish the nation's major rivers pushed under the Lee Myung-bak administration.

Those included were Doosan E&C, Hanjin Heavy Industries and Construction Co., Samwhan Corp., Hall Engineering & Construction Corp. and Kyeryong Construction, which joined a consortium to earn the river project. 

Earlier in the day, investigators were dispatched to headquarters of the companies to look into their computers and documents, according to company officials.

The probe comes after opposition lawmakers last year raised allegations that local construction companies colluded in the bidding process, leading to an unfair competition.

Last year, the FTC imposed a fine of 111.6 billion won ($103.4 million) on six other major construction firms, which were accused of colluding in the river project.

The latest move comes as the Park Geun-hye administration is looking into the multibillion dollar project pushed under the previous government, which faced opposition by civic groups and environmentalists.

The river project has emerged as a hot political issue after the Board of Audit and Inspection announced in January that construction work was so shoddy that a number of serious problems have arisen, such as damage to weirs and structures that were built to strengthen riverbeds. (Yonhap News)