There's a legal requirement to comply to emissions laws. Is there a legal requirement to make it easy for cops to use your service? Are they a protected class?

There's a legal requirement to comply to emissions laws. Is there a legal requirement to make it easy for cops to use your service? Are they a protected class? If I didn't want to sell donuts to the cops, I sure wouldn't tell them it's because they are cops. I would just be mysteriously out of donuts every time they come in.