If you’re recruiting for your next employee on Facebook, you may be doing it wrong—according to the law.

This week, ProPublica and The New York Times exposed a serious issue involving many major companies. To put it simply: The companies were recruiting employees using Facebook’s advertising tools. Among the ad-targeting tools these companies used were age restrictions, something that is illegal under U.S. law, with the Age Discrimination in Employment Act of 1967 specifically prohibiting bias against people over age 40 in recruitment practices.

Facebook disputed ProPublica’s reporting on the issue, stating that simply targeting advertising to desired age groups, as is common in digital advertising, is not the same as discriminating against people in hiring practices.

“U.S. law forbids discrimination in employment based on age, race, gender, and other legally protected characteristics,” the company’s vice president of ads, Rob Goldman, wrote in a letter to the nonprofit news outlet. “That said, simply showing certain job ads to different age groups on services like Facebook or Google may not in itself be discriminatory—just as it can be OK to run employment ads in magazines and on TV shows targeted at younger or older people. What matters is that marketing is broadly based and inclusive, not simply focused on a particular age group.”

ProPublica’s reporting, however, raised concerns that many job seekers would not even be aware of the positions because of the targeted advertising. The media outlet’s inquiries led one major social network targeted at professionals, LinkedIn, to change its system to discourage misuse for this specific reason, though another company, Google, said it did not block advertising based on age restrictions in any form.

And it could lead to legal action. On Wednesday, the Communications Workers of America, a labor union, filed suit against Facebook, seeking class-action status for the network’s users over age 40 who would have been negatively affected by these measures. The union cited cases in which T-Mobile used such ads to target people ages 18 to 38 to work at its retail stores.

The issue highlighted by the story is complicated, and not everyone felt that what was happening was as serious as was being reported. Some companies saw the targeted advertising approach as akin to advertising in multiple magazines targeted at different age groups.

But whatever the case, the issue promises to be one that gains attention in the coming months—and if you’re hiring, it’s worth understanding the legal implications of such targeting.

(HStocks/iStock Editorial/Getty Images Plus)