I could easily see this Quran-burning pastor suing on the grounds that he was discriminated against.
How could he claim that? Federal law forbids discrimination in hiring based on religion, but that doesn't mean once I hire a Muslim worker because of his ability to perform the job I have to allow him to take out a rug, kneel and pray for an hour each day while on the clock. He still has to play by my rules, which are applied equally to everyone.
Still, this is not that. This isn't a guy quietly practicing his faith and sharing it peacefully with others. To hear some people say it, he's honestly inciting violence. He's being willfully, dangerously provocative.
Wouldn't be surprised if he did find a lawyer to buy him a few more minutes in the spotlight. Interesting angle, and one I hadn't thought of. Ugh, dealing with people: at once the best and worst part of business.
However, the "business relationship is a two way street" theory has some caveats. While many of us are familiar with the "We reserve the right to refuse service to anyone" signs in brick and mortar stores, it's not always that simple.
Take the wedding photographer who was sued (and lost) for refusing to photograph a same-sex wedding: http://www.cbn.com/CBNnews/357084.aspx
Obiviously, these examples aren't entirely analogous, but given the litigious nature of American society, any time you refuse/halt service to a customer, it has to be considered. I could easily see this Quran-burning pastor suing on the grounds that he was discriminated against.