From Spero News:

The complainant (known only as Shelton D.) said that as of the fall of 2013, a coworker frequently wore a cap in the workplace that displayed the famous Gadsden Flag, which depicts a coiled rattlesnake and the motto “Don’t tread on me.” The flag is beloved by patriotic groups, reenactors, the military and others.

According to the complaint, the cap is racially offensive to black Americans because it was designed by Christopher Gadsden, who was described as a “slave trader & owner of slaves.” After management told the complainant that the coworker had been told to refrain from wearing the cap, the coworker continued to work while wearing the cap. The complaint ensued.