Depends on what agreements are in place. In this case the CBA. Lawsuits of this nature are usually centered around breaking your own bylaws.
I doubt Hardy would stand a chance in court arguing that his punishment is inconsistent with Irsay's (if he get's punished).
Irsay was suspended 6 games and fined $500k but it didn't happen until his legal case was concluded. Hardy should get the benefit of the same policy granted to the owners.