Prosecutors probing a tax evasion case involving construction firm Mizutani Kensetsu Co. have questioned employees of general contractor Obayashi Corp. in connection with an airport project it subcontracted to Mizutani, according to investigation sources.

Mizutani posted sales of 10 billion yen from projects related to the construction of Central Japan International Airport outside Nagoya in the business year through August 2003, when then company Chairman Isao Mizutani, 61, allegedly evaded 230 million yen in corporate taxes, the sources said Tuesday.

Mizutani mainly handled land development projects at the airport, also known as Centrair, and Chubu, under its contract with Obayashi.

The prosecutors asked the Obayashi officials for details about the contracts with Mizutani and the process through which the deals were made, the sources said.

Mizutani was also involved in such construction projects as the Kido Dam and the No. 2 nuclear plant of Tokyo Electric Power Co., both in Fukushima Prefecture, as a subcontractor of major builders, the sources said.

As part of efforts to probe why Mizutani was able to win so many deals, the prosecutors have questioned officials of major construction companies like Taisei Corp. and Kumagai Gumi Co. that failed to win bids for the projects, the sources said.