Keith Burris was at the center of the firing of cartoonist Rob Rogers and penned the "Reason as Racism" editorial.
The union has a contractual right to its bulletin boards.
Post-Gazette employees said the Saturday incident included classist insults and threats of firings.
The newspaper won't publish this letter, which says the work of Rob Rogers' replacement "display[s] a contempt for women and an obvious deep-seated prejudice against them."
Pittsburgh Post-Gazette publisher refuses to print in-house criticism of ‘Reason as racism’ editorial
The list of critics grows: Newsroom employees, former journalists, two foundations — and the publisher’s own family and friends.