TOKYO, (REUTERS) - Japanese regulators said on Friday (March 23) that they would press criminal charges against four construction firms for suspected collusion over contracts for a US$80 billion (S$105 billion) high-speed magnetic levitation (maglev) train line.

The firms include Taisei Corp, Kajima Corp , Obayashi Corp and Shimizu Corp. The Japan Fair Trade Commission said it would also press criminal charges against an official at Taisei and another at Kajima.

A Shimizu spokesman told Reuters the firm was deeply sorry and that the incident was regrettable. Kajima said in a faxed comment it was taking the charges seriously and that it was deeply sorry for causing trouble.

A Taisei spokesman said in an email that the firm did not think the case violates anti-trust laws, although it was taking the incident seriously. Obayashi said it was still looking into the charges.

Prosecutors and anti-trust agency officials have been investigating the so-called "big four" group of Japanese construction firms for suspected antitrust breaches relating to the high-profile maglev project since last year.

Japan's large and politically influential construction industry has been a frequent source of scandals such as bid-rigging.

Legislation has been tightened in recent years to prevent collusion over contract bids, and Obayashi in 2006 required managers to sign a pledge to abide by antitrust laws. The next year, however, the firm's top management resigned following a public works scandal.