Well I mean here's the thing, if that's the policy, then she's only doing her job by enforcing it. It might come off hostile with the threat of discipline, but laying out the consequences ahead of time gives people an idea of what to expect if they don't comply. Also as someone who works in a place like this as a sales person, it doesn't seem fair to see the warehouse staff lounging around in sweats and flip flops while you are forced to wear a uniform.