And you won’t be able to do anything but ask because you are not a police officer. ISP isn’t a court and restaurant operators aren’t officers of the law.
You can for any reason, unless the reason is discrimination against a protected class. But do not pretend that it is for breaking the law, because it's only up to the court to determine whether I broke a law or not.
So if AT&T want to disconnect a customer for an arbitrary reason, fine: but they need to make it more clear initially, while considering their utility status.