Can I un-sign company policy paperwork?

I took the humiliating random drug test. The paperwork stated if I didn't I would be terminated. I don't do drugs and have worked at the company for a very long time so I know it will be clean. In CA, the law states we can say no to drug testing (unless you're a gov. employee working for the DOT). Can send my HR an e-mail revoking my permission to take any more random tests? Without just cause I would consider it to be harassment.