Anthony Bottalico, head of the Association of Commuter Rail Employees, made the announcement about William Rockefeller's status a day after the National Transportation Safety Board booted union representatives from the crash investigation, WPIX-TV, New York, reported Wednesday.
Bottalico said Tuesday Rockefeller "basically nodded" off while at the train's controls.
Rockefeller is unlikely to face criminal charges if his only crime is falling asleep, said Justin Green, an attorney who specializes in transportation accidents.
However Green said he expects Rockefeller "never works again as an engineer and probably not for the [Metropolitan Transportation Authority] going forward."
Bottalico said the union continues to provides Rockefeller with legal representation.