The District of Columbia Circuit Court of Appeals recently suspended the implementation of the NLRB's recent rule requiring employers to post what is effectively a union endorsement notice in virtually every workplace (see the discussion below, here). In doing so, the Court of Appeals very sensibly determined that there was some confusion about a lower federal court ruling that suspended the enforcement mechanism of the NLRB rule, but allowed the posting requirement to go forward. The Court also noted a recent South Carolina federal court decision that invalidated the rule in toto as a basis for enjoining the application of the posting requirement.
So as of now, and until the Court of Appeals gets through the issue, employers do not have to put up the new NLRB poster. I'm guessing it will take at least a year for the briefing and oral argument to be completed, and perhaps another few months after that before a decision issues.