It does happen. Here is a December 2013 article.
The NTSB said late Tuesday that the board removed the Association of Commuter Rail Employees (ACRE) from its status as a participant in the investigation over a press conference held earlier in the day by the union’s general chairman, Anthony Bottalico.
At the presser, Bottalico admitted that the train’s engineer, William Rockefeller, had dozed off moments before the derailment, which occurred at a sweeping curve in the track near the Spuyten Duyvil station on Metro-North’s Hudson Line.
The NTSB Release stated:
The National Transportation Safety Board today removed the Association of Commuter Rail Employees, or ACRE, as a participant in its investigation into the December 1 derailment of a Metro-North passenger train in the Bronx, N.Y., that killed four people and injured dozens.
Under the NTSB’s procedures, organizations and agencies are invited to provide technical expertise in support of the NTSB’s investigation. The organizations designated as parties sign an agreement to abide by NTSB rules for the duration of the investigation. Maintaining confidentiality of investigative information is one of the rules that parties agree to, further, they agree that their organizations will neither reveal nor comment on investigative information.
On Tuesday, December 3, Anthony Bottalico, General Chairman of ACRE, conducted a press conference and a series of media interviews during which he discussed and interpreted information related to the on-going investigation. As a result of this violation of the party agreement, the organization was advised tonight that it was removed from the December 1 Metro-North train derailment investigation.
“While we value the technical expertise that groups like ACRE can provide during the course of an investigation, it is counterproductive when an organization breaches the party agreement and publically interprets or comments on investigation information,” said NTSB Chairman Deborah A.P. Hersman. “Our rules exist to avoid the prospect of any party to an NTSB investigation offering its slant on the circumstances of the accident.”
Article on MetroNorth