The general rule is that a restaurant has a right to refuse service to anyone at any time, but that rule isn't going to extend to discrimination. They can't, for example, let a 40 person group of one race stay and ask another to leave if you aren't being loud or disturbing other customers (and if you had your own room, that shouldn't have been an issue). Discrimination based on group size would be OK, but not based on race, ethnicity, religion, or something like that. So you may have a case against them for discrimination if they didn't put a maximum limit on your group, didn't ask other, equally large groups to leave, didn't set a time limit when you arrived, and didn't warn you that there were noise issues or other complaints before asking you to leave. Any any person who did not get to eat because they chose to send the whole group out is entitled to a full refund of the monies paid.
If there is a person above the person who asked you to leave, that might be a starting point for someone to talk to who could make this right. Or if the restaurant is a chain, you could send a letter to the corporate office - both the Customer Service division and the legal department. They might be willing to work with you in order to avoid the negative publicity of a lawsuit. If they won't, then you may want to talk to a local attorney about helping you take things further.
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