Recent unfortunate news headlines prompted a quick search for the almost universally un-cited regulations governing passenger compliance with flight crew, and all I could find were regulations that seem to be quite specific in application (14 CFR 125 - interference, etc.).
While it makes sense that passengers are expected to comply with reasonable requests, one would not expect the law to require compliance with unreasonable requests unrelated to safety, or requests that actually endanger passengers.
So, for example, if a crew member requests that a seated and non-disruptive passenger leave a plane for purely commercial reasons unrelated to anyone's safety, is there a law or regulation that supports this for US carriers?
Again, I expect the answer is "yes," but am interested in the legal basis for it, and do not think the self-serving fine print on an airline ticket qualifies.