(Corrects third paragraph regarding date of special meeting. Shareholders as of March 16 are eligible to vote in the special meeting, which has not yet been scheduled) By Allison Lampert and Ankit Ajmera Feb 21 (Reuters) - U.S. railroad operator CSX Corp's chief executive, Michael Ward, will retire after more than 14 years in the role, as activist investor Mantle Ridge LP tries to shake up the company's board. Mantle Ridge, which has a 4.9 percent stake in CSX, has been pushing the company to name Hunter Harrison, former CEO of Canadian Pacific Railway Ltd and a turnaround expert, to the top job. Last week, CSX said its board had called for a special shareholder meeting in the spring to vote on Harrison's proposed pay package, which is estimated to exceed $300 million, and discuss other demands made by the hedge fund. Shareholders as of March 16 are eligible to vote in the meeting.