(Reuters) – Several U.S. employers engaged in age discrimination by placing recruitment ads on Facebook targeting younger workers, according to a lawsuit filed on Wednesday by a communications industry labor union.

Companies including T-Mobile US Inc (TMUS.O), Amazon.com Inc (AMZN.O) and Cox Communications Inc imposed age limits on who could see recruitment ads, limiting some only to people younger than 38, according to the lawsuit, filed in federal court in San Francisco by the Communications Workers of America.

“This pattern or practice of discrimination denies job opportunities to individuals who are searching for and interested in jobs, reduces the number of older workers who apply for jobs with the offending employers and employment agencies, and depresses the number of older workers who are hired,” the complaint reads.

The lawsuit is the latest example of criticism leveled at Facebook for so-called micro-targeting, a process that has allowed advertisers to choose who sees their ads based on age, interests, race and even such characteristics as whether they dislike people based on race or religion.

Last month, the company said it was temporarily disabling the ability of advertisers to exclude racial groups from the intended audience of ads, and promised to “do better” at policing discriminatory practices.

Facebook, which is not named as a defendant but is accused in the lawsuit of engaging in the practice in its own recruitment efforts, said in a statement on its website that it does not engage in age discrimination.

A giant logo is seen at Facebook’s headquarters in London, Britain,…