First, record everything if you want to instigate legal action, but here's the gist.

You don't have to wear the mask. You are exempt. If they ask you why you are exempt, you can simply tell them for medical reasons. If they ask you you're medical reasons, you CAN SUE due to the HIPAA (Health Insurance Portability and Accountability Act of 1996). If they discriminate against you and ask you to leave or accept service outside or some faggy shit, you can get them fined for discrimination. Its a $75,000 fine.

EDIT: Be sure to upload the footage of mask traitors to bit chute, rumble, or gab.tv