The Fair Trade Commission conducted on-site inspections of four companies on Tuesday over suspicions they were involved in bid-rigging for expressway cleanup contracts in violation of the antimonopoly law, it has been learned.

Among the four Japanese road maintenance companies are Subaru Enterprise, which is listed on the Tokyo Stock Exchange's Standard section, and Nihon Highway Service, according to informed sources. The companies' head offices and other locations were searched.

The firms are suspected of engaging in bid-rigging for Metropolitan Expressway orders for the cleanup of expressways managed by the Tokyo-based company.

The FTC plans to analyze seized materials and interview people concerned, suspecting that competition for road cleaning services may have been virtually restricted due to the four firms' alleged malpractice.

According to the sources, the four companies have allegedly predetermined winners of Metropolitan Expressway orders for at least several years.

Bidding was held every two years for four expressway sections, with each order worth around more than ¥1 billion to ¥2 billion per section. The companies are believed to have coordinated to ensure that each firm could continue to win orders for the same section so that they can make stable profits, according to the sources.