I tell potential clients all the time that they can be fired for anything – so long as the cause is not related to potential discrimination. One construction worker learned that lesson the hard way. An employee of a subcontractor who was working on the new stadium at Texas A& M was fired because he displayed the wrong flag. He flew the Alabama Crimson Tide flag atop the stadium. That was probably not a wise thing to do in the middle of Aggie country…..
That is what the at-will doctrine is all about. A worker can be fired for any reason. See San Antonio Express News report.