I would be willing to bet that in the employee handbook it requires that nobody act in a nature that is contrary to the advancement of the company. This most certainly is, and is also likely easily cited as a lack of productivity of the employee while being paid by the company.
Illegal policies are not enforced by courts. For instance, forced arbitrarion clauses, no discussions of wages, non-disparagement (Does your company say you aren't allowed to say negative things about the company, whether online or otherwise? Again, this probably violates your right to discuss working conditions), confidential information (if it violates your right to discuss working conditions), or social media prohibitions (if the company social media policy says you aren't allowed to discuss or disparage the company in social media, that may well violate your right to complain about working conditions)
