Is this Legal?? Please Help Me!?

So a few months back my employer decided to invest in a security cameras for "our safety" yeah right. These cameras have been an option to keep an eye on us. Just recently they fired 2 people from my department, and numerous others. Anyway... We found out these cameras have audio. 1. Is this legal for them to have audio and have my superior tell certain people, including me to watch our mouths? 2. They just recently installed a camera right in front of the females/males restroom. I have to wear a uniform which I have to take off when entering the restroom and I have this camera looking at me taking my uniform off (which I have my regular clothes underneatht) but it makes me feel very uncomfortable, and creepy. Is this legal for my employer to do this? I mean I understand watching us on the floor but next to the restroom. When I commented this to my boss, he took it to his supervisor. You wanna know what his supervisors answer was? "If they don't like it, the doors open for them to leave" My jaw dropped. Can someone PLEASE HELP ME!?!?!? Is this legal???

The only people that have access to these cameras are High ranking supervisors, which are all MEN! To top it off they have access to these cameras from home!!! If it helps in live in the state of Nevada.