Yeah, learning to tell cops “no” is actually a fairly large part of off-the-books EMT training. It’s not something officially trained, (because nobody wants to be the one to put it in an official handbook and earn the ire of every cop in America,) but it’s something every new EMT gets drilled on anyways.
Because there will be times when you’re the only thing standing between your patient and a belligerent cop. And in that situation, you have a duty to care for your patient, even when the cops are yelling at and threatening you personally.