The complicated, unanimous decision written by Justice Stephen Breyer essentially gives the president recess appointment power only when the Senate is formally adjourned, but does not apply during the chamber’s so-called pro-forma sessions, when no official business is being conducted but the Senate is not officially in recess.

Noel Canning v. National Labor Relations Board, which prompted the Supreme Court decision, challenged President Barack Obama’s appointment of three National Labor Relations Board members during a brief Senate break in 2012. The ruling found that President Obama overstepped his authority in making the those appointments, and it invalidates the hundreds of decisions made by the subsequent board from January 2012 through July 2013 because nullifying the appointments of three of the members on the board at that time takes away the quorum the five-member board needs to decide any case.

And it just so happens that during that time frame, the NLRB handed down starkly pro-employee decisions that its current members must now reassess.

Most notably, the board decided that Costco’s (COST) electronic communications policy, which banned employees from publishing social media posts that “damage the company, defame any individual or damage any person’s reputation,” unlawfully restricted employees’ protected rights. The decision protected workers from being fired for badmouthing their employers on sites like Facebook (FB).

Another NLRB ruling in a case involving Banner Health Systems banned employers from demanding that a worker who is the subject of an internal investigation refrain from discussing the inquiry with his or her colleagues. That sort of confidentiality requirement had been typical in, say, investigations into allegations of sexual harassment, says Daniel Johns, an attorney who represents employers in labor and employment disputes for law firm Ballard Spahr. And the NLRB’s ruling in Banner Health “reversed a 30-year precedent,” says Joel Barras, a labor and employment lawyer at Reed Smith.

The 2012 board also issued decisions that have been interpreted as union-friendly, including a decision related to a Gannet-owned television station in Cleveland in which the NLRB determined that an employer is required to deduct union dues from employees’ paychecks even after a union contract expires.

The NLRB, whose job it is to conduct union elections and address unfair labor practices, has “issued a number of decisions that are exceedingly favorable to unions and employees,” Barras says.

So, does Thursday’s decision mean that those pro-employee decisions will be undone for good?

Not necessarily. In 2013, the Senate approved five new NLRB members following a deal in which Senate Republicans agreed not to filibuster executive branch nominees in return for White House nominations of two Republican picks to the board.

Even with the Republican members, however, the overall makeup of the board is still decidedly pro-labor, so there’s a good chance that even though the new board must rehear the cases from 2012 and early 2013, the ultimate outcomes may not be different.

But until that happens, those far-reaching employee-friendly decisions are null and void. “As we sit here today,” Johns says, “they’re no longer in effect.”