1. they can test for nicotine but not tobacco*
2. most places in US are "at will" employment so they can fire for any reason or no reason, as long as it's not in violation of the civil rights act

that being said if they're being niggers about it you should claim that you have an addiction (a legally protected disability) and they have to send you to rehab. maybe they don't do it but they should know that fucking with you will get very expensive

https://youtube.com/shorts/yxnIf3UNHx8

* edit to add: I mean chemically they can test for nicotine, but there is not a test for tobacco specifically