Burbank police detectives are investigating the threat, Sgt. Stephen Turner told The Times. No arrest has been made, and no additional information about the letter is being released at this time, he said.

The letter, which the industry website Puck characterized as a “death threat,” closed the IATSE office Friday. DeJon Ellis Jr., IATSE’s business manager, told Variety that the letter, allegedly written by a grip struggling with unemployment, was postmarked Wednesday and primarily addressed to Local 80, which represents grips and below-line workers.

IATSE is not on strike, but many of its members are unable to work because of productions shut down by strikes by the Writers Guild of America and SAG-AFTRA.

Repsentatives for IATSE did not immediately return requests for comment Saturday. In addition to Local 80, the national union temporarily closed its West Coast headquarters, also in Burbank. Justine Bateman tweeted (and then deleted) a post that said a weekend panel discussion scheduled at Local 80 had been canceled.

The economic impact of the writers’ and actors’ strikes, while broadly supported by industry workers, has been felt not only collectively in the L.A. economy but also individually by tens of thousands of actors, writers and film crews who are unable to work. The Entertainment Community Fund, which supports out-of-work film and TV professionals, has distributed more than $4.7 million since May 2.