Keep an journal of how they are treating you. Note any treatments of the other employees that show your treatment to be discriminatory. Go ahead and sign the document. Be careful with your emails. And.... Maybe you should start looking for other work. In the mean time, stick it out and make them let you go. In time, they will likely mess up and you will have a strong case to file.

You can create a written history by responding to verbal issues in writing. An email such as, "I am willing to sign document xyz but it appears I am the only one being asked to sign document xyz. Can you help me understand why I am being singled out for this treatment ?" You may want to be less confrontational. Maybe " I am confirming that I am the only one being asked to sign document xyz. Is this correct ?" Then, print a copy of the email for your personal files and take it home.

My best to you.