The activist investors trying to take control of Norfolk Southern’s board are picking up key support, but the railroad’s CEO promised Monday to fight the takeover attempt until a May 9 shareholder vote because he believes his strategy is the best in the long run for investors, customers and workers.

Ancora Holdings’ bid to elect seven new directors and replace management at the Atlanta-based railroad has gained the backing of one of the major proxy advisory firms, one of the railroad’s biggest customers and two of its largest labor unions in recent days.