"Employment relationships are presumed to be “at-will” in all U.S. states except Montana. The U.S. is one of a handful of countries where employment is predominantly at-will."

https://www.ncsl.org/research/labor-and-employment/at-will-e...

Anything (or nothing) in the US can be a fireable offense, so I wouldn't worry too much about what you put on a resume.