Someone on my staff is an avid Bernie Sanders supporter who is trying to get other employees to participate in protests against Donald Trump. Does she have the right to free speech, or can I prevent her from doing this?

This is an outrage, unless she is also going to organize a protest against Hillary! (Oh, c’mon . . . we need a little more political humor and less rancor!) Generally, an employee’s politics and political activity outside of work are off-limits to employers — unless that activity reflects poorly on the company. As for conduct in the workplace, employers may impose all kinds of restrictions and bans on speech and conduct. They can ban solicitiation of any kind (yes, even for Girl Scout Cookies), wearing or posting slogans, etc. And if they exercise their free speech to proselytize their political beliefs, co-workers have a right not to be subjected to that speech — and employers can ban it, and are within their rights to discipline employees who disregard any of those rules. But before you threaten your employee with disciplinary action, just tell her that it is fine for her to feel the Bern outside of work, but that is where it needs to stay. And if she challenges that decision, explain to her that the company has the right to subject her to “yuge” consequences if she doesn’t comply!