Can I be drug tested after 2 years of employment?

Hi, I've been working for a company for 2 yrs. Recently there was a disgruntled employee issue who made an idle threat. It was taken serious because you have to these days. Because of that some managers have decided that everyone in the company and new hires should be drug tested. I understand the new hires, they will be told as a condition of employment, but what about the rest of us? Some of us have worked for 10 yrs with this company, without this policy. Is there some protection for us? Thank you.