Answers all of the op's posts in one place!!!
OK, here are your answers all in one place. However, they're only accurate if you're in the US.
It's legal for your employer to ask you to you sign a document you don't agree with.
It's legal for your employer to fire you if you don't sign a document you're asked to sign (whether you agree with the document or not).
It's legal for your employer to allow you only one bathroom break during a four-hour work period, unless you can provide a doctor's note stating you require more bathroom breaks during a four-hour work period.
It's legal for your employer to require you to bring a doctor's note in after sick leave (of any duration - from one minute to whatever), even if you don't have health insurance or money to pay a doctor.
It's legal for your employer to fire you for not bringing in a requested doctor's note.
It's legal for your supervisor to harass you all the time, as long as the harassment is not based on things like your race, gender, religion, and so on. If this harassment is based on things like your work performance, or the type of sneakers you wear, or the coworkers you talk to, or the number of bathroom breaks you want to take, or because your supervisor simply doesn't like you, then it's legal.