The best advice I can give is to ensure you have open-minded faculty members at your back. If you have professors you feel you can talk to, I would try to have a casual conversation with them as soon as you can. Their advice and backing will be invaluable, if and when a formal situation arises.
In the US, under at-will employment, an employee "can be dismissed by an employer...without having to establish 'just cause' for termination..." [1]
If you'd prefer a different standard because this rule sounds harsh against employees, think for a moment from a company's standpoint: If you know the law won't make it easy for you fire someone, you'll be really picky about who you hire, how you hire them, and how many people you hire.
I think at-will employment helps everyone by making the job market more liquid and reducing the size of the class of "unemployable" people.
Fair enough to say 'that these show bigger issues with the company and you'd be better off elsewhere' but it doesn't stop companies like these existing and minimising the cost to them isn't something I particularly support.
P.S. I think the reply to your comment by lvs has some good thoughts.