You don't get free speech at any job. You represent the company and its interests or you quit or get fired. It's common sense, a good work ethic, and called being an adult.
It is the League's job to police the teams and the teams' to police their players and employees. The league should suspend any team's franchise that blatantly allows its employees to jeopardize its wellbeing, if not its very existence. It reasonably follows that those players who attempt to deliberately hijack their workplace should be fired, banned from playing, and possibly have to buy out their contracts.