"Expanding Rights under the “Retaliation” Provision of Title VII. Title VII of the Civil Rights Act of 1964 (the “Act”) prohibits an employer from retaliating against an employee who has “made a charge, testified, assisted or participated in” any charge of unlawful discrimination under the Act."

http://www.sgrlaw.com/ttl-articles/826/

Words are defined by how people use them, and this fits the common usage of the word illegal.

Nobody cares what pedantic definition a lawyer would use to describe this, because nobody made lawyers the language police.