Last month, the National Labor Relations Board found that colleges that tried to block football players from posting freely to social media and speaking to the media were overstepping their legal bounds.

But far more important than the NLRB’s free-speech stance was a footnote at the end of the memo that classified the football players as “employees.” That characterization is creating deep concern at Northwestern University and 16 other private division 1 colleges that fear that their athletes will soon have the opportunity to unionize, costing the schools millions of dollars.

Though the NLRB wrote the memo last month, its full text was released only in the past week—and it is now being heavily analyzed and discussed. Unionization would be an expensive change, not just for Northwestern, whose athletes have been pushing for that for two years, but for Stanford, Duke, Notre Dame and other private schools known for their athletics. (The NLRB exercises jurisdiction over private companies, including private universities, but not public-sector employers.)

In 2015, the NLRB declined to decide whether Northwestern athletes could form a union, overruling a regional office ruling that had supported the football players’ attempts to organize.

Odd enough, Northwestern football players were not the ones challenging their university’s speech restrictions. Instead, the complaint was brought by an activist California labor lawyer and Berkeley professor, David Rosenfeld, who had no ties to Northwestern or its players.

The speech restrictions in Northwestern’s handbook allowed Rosenfeld to bring a complaint that would, in practice, push the NLRB to acknowledge college athletes as employees, not just students. “It’s moving the law in the right direction, which I thought I accomplished,” Rosenfeld tells Heat Street. “It’s more about treating them as employees. It’s not really a speech issue. It’s [about] a right to organize and improve the workplace.”

Already, Rosenfeld adds, he’s heard from an interested athlete at Stanford.

Earlier this year, the NLRB found that graduate students at Columbia University counted as employees under the National Labor Relations Act, opening up the possibility of unionization to more than 500,000 graduates attending private colleges and universities in the United States.

A spokesman from Northwestern said the university disagrees with the NLRB’s classification of scholarship-receiving football players as employees, saying it considers them “students, first and foremost.”

Though Northwestern believed its original speech guidelines were lawful, to get the complaint dropped, the university revised its handbook for football players.

Before, Northwestern explicitly forbade any post that could potentially embarrass the football players, their families, their team or Northwestern and its athletic department.

The university now restricts only social-media posts that include “harassing, unlawful or dangerous behaviors such full or partial nudity (of yourself or another), sex, racial or sexual epithets, underage drinking, drugs, weapons or firearms, hazing, harassment, or unlawful activity.”

The NLRB’s memo also prompted Northwestern to change its policy allowing athletes to accept only interviews arranged through the university’s media office. Now, football players can speak to journalists if they want, without advance permission.

Jillian Kay Melchior writes for Heat Street and is a fellow for the Steamboat Institute and the Independent Women’s Forum