Major Japanese construction company Obayashi Corp., which is at the heart of a scandal over collusion in bidding for a maglev train link project, has decided to take a rare and pre-emptive step: Come clean about its role, and possibly evade criminal prosecution.

Ahead of the "plea bargain" system set to be introduced next year, sources close to the matter said Tuesday that Obayashi has admitted to the Japan Fair Trade Commission its involvement in bid obstruction with three other major contractors — Taisei Corp., Kajima Corp. and Shimizu Corp. — exempting it from a fine under the commission's leniency rules.

Prosecutors are keen to use the plea bargain arrangement to make progress in exposing criminal cases, but there are concerns about heavily relying on this method.