The Japanese company, which paid a record fine a year ago for its bookkeeping practices, warned that it may now have to take another charge of several billion dollars related to an acquisition made by U.S. unit Westinghouse Electric. The company’s shares fell 12 percent to 392 yen at the close in Tokyo on Tuesday, the biggest decline since December 2015, after earlier reports that it may book a loss of as much as 500 billion yen .