In a memo to the heads of executive branch departments and agencies (the memo can be found here), Reince Priebus, President Trump’s chief of staff, ordered a freeze on all pending regulatory actions except those addressing “emergency situations or other urgent circumstances relating to health, safety, or national security.”
Under the freeze, agencies may not submit regulations for publication in the Federal Register. Alternatively, for any regulation that has been submitted for publication but not yet published, the agency must withdraw it from the Office of the Federal Register.
The order is a standard step taken when the party of the incoming administration differs from that of the departing administration. Virtually identical memos were issued by Presidents G.W. Bush and Barack Obama soon after their inaugurations.