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TOKYO (Reuters) - Tokyo prosecutors raided the headquarters of Japanese construction firms Taisei Corp 1801.T and Obayashi Corp 1802.T on Tuesday over alleged antitrust violations linked to $80 billion worth of magnetic levitation (maglev) train projects.

Shares in Taisei fell 5.3 percent to a more than 3-month low, while Obayashi shed over 3 percent before paring losses. The benchmark Nikkei average .N225 was flat.

Taisei, one of the so-called “big four” of Japan’s construction firms, is fully cooperating with the investigation, company spokesman Takayuki Renbutsu said.

Separately, prosecutors raided Obayashi’s offices over suspected antitrust breaches, a company spokeswoman said. The firm is already under investigation for suspected bid-rigging over maglev-related contracts.

The Tokyo prosecutor’s office said it could not comment on individual cases.

The raids come after prosecutors launched investigations into Shimizu Corp 1803.T and Kajima Corp 1812.T, also on alleged antitrust breaches related to the maglev project. The train line will link Tokyo, Nagoya and Osaka.

Shimizu shares fell as much as 3.2 percent, while Kajima slumped as much as 5.6 percent, both extending losses from Monday.

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