Fox News was one of a few media networks to receive threatening letters on Wednesday.

Fox News host Bret Baier did a reportabout the letters during his evening show, “Special Report.” He said that the Fox News headquarters in New York City received one such letter, which included a warning that said some envelopes could contain a lethal pathogen. The letter would also include the return address, “The MIB.”

Letters were also sent to Jon Stewart and Stephen Colbert. The letters included claims that more were sent to The New York Times and NPR.

Reports indicate that the letters were sent from Portland, Oregon.