Is it illegal to fire an employee for complaining about a protected activity?

Title VII (and many other laws) prohibit employers from discriminating as well as retaliating against employees who engage in protected activities, such as reporting or opposing unlawful employer behavior. Henson v. Canon Bus. Sols., Inc., 69 F. Supp. 3d 730, 737 (N.D. Ill. 2014)

A retaliation claim can be shown by proving that an employee  (1) she engaged in a statutorily protected activity; (2) that Canon took an adverse employment action against her; and (3) a causal connection between the two. Coleman v. Donahoe, 667 F.3d 835, 859 (7th Cir.2012).   Depending on the context, a plaintiff must prove that but for the protected act, he or she would not have suffered the adverse employment action.   

A plaintiff may present “smoking gun” direct evidence of causation which requires “something akin to an admission” of retaliation by an employer. A plaintiff may also demonstrate the requisite causal link by constructing a “convincing mosaic” of circumstantial evidence, relying on “suspicious timing, ambiguous statements […], and other bits and pieces from which an inference of retaliatory intent might be drawn.” Id.   Henson v. Canon Bus. Sols., Inc., 69 F. Supp. 3d 730, 739–40 (N.D. Ill. 2014).

Different laws require different proof to prove a retaliation claim.