The NTSB said it has booted the rail union from its investigation into the weekend's deadly train derailment for violating confidentiality rules.
The agency made the announcement late Tuesday night, hours after a union representative told CNN that the train engineer apparently "was nodding off and caught himself too late" before the accident.
The train derailment Sunday killed four people and injured 67 others in New York.
In its announcement, the NTSB specifically cited those comments as the violation.
Anthony Bottalico, the union representative, told CNN that engineer William Rockefeller Jr. recognizes his responsibility in the incident.
"I think most people are leaning towards human error," Bottalico said.
Rockefeller's lawyer, Jeffrey Chartier, characterized what happened as "highway hypnosis." He said his client had had a full night's sleep before the crash, and had no disciplinary record.
In a brief conversation with investigators, Rockefeller said that moments before the derailment of the Hudson Line train in the Bronx he was "going along and I'm in a daze. I don't know what happened," according to a law enforcement official familiar with that conversation.
Rockefeller spoke to Metropolitan Transportation Authority and New York Police detectives at the crash site before he was taken to the hospital Sunday.
According to NTSB representatives, results from alcohol breath tests for the train engineer were negative, and the brake and signal systems in the deadly Metro-North accident appeared to be working. Other toxicology results have not yet come back.
Fatigue is a factor being investigated, according to a separate New York law enforcement source. But Rockefeller also told investigators on site that the brakes had failed, as CNN reported previously. Officials noted the train had been able to stop nine times at stations ahead of the crash.
The train was equipped with a "dead man's pedal," designed to stop the train if the engineer becomes incapacitated, said National Transportation Safety Board member Earl Weener. But it was unclear whether that emergency system was activated.