TOKYO—A retired Olympus Corp. executive and director is trying to rally company employees behind a campaign calling for the return of ousted chief executive Michael Woodford, in the first sign of disaffection with current management from inside the scandal-ridden company.

The effort is being led by Koji Miyata, who Saturday posted online an open letter to Olympus employees, urging the speedy reinstatement of Mr. Woodford, who had been fired last month after raising alarms about possible fraud. Mr. Miyata said in an interview...