Can you get in touch with the branch manager? Will he/she be there tomorrow? There is no way they can fire you for trying to follow the law and protect the store from liability. If the store manager won't back you up, you need to keep taking this up the chain, to the point of calling corporate if necessary. I know this has put you in a very bad position as far as having a comfortable work environment, but this is absolutely ridiculous, and somebody who is going to give a shit needs to know about this.