The following is is a list of things that employers often do, which might seem unfair or hurtful, but generally not illegal (in the absence of specific evidence of discrimination or unlawful retaliation) in an at-will employment setting:
(1) Issuing unfair performance reviews or warnings
An employer is entitled to a subjective view and opinion of your job performance. The fact that you disagree with your review or believe it’s false or unfair, and the fact that you think that you are very good at what you do, doesn’t make that evaluation illegal. The same applies to warnings or any other disciplinary action.
(2) Hiring / promoting friends or relatives.
It’s not against the law for a manager to hire or promote a friend or a relative over another employee. This is different from treating someone more or less favorably because of their race, age, disability, gender, religion, etc.
(3) Changing your job duties / not providing training.
Changing an employee’s job duties, however different they might be from the ones initially provided in that employee’s job description is not illegal. The fact that you believe these duties are incompatible with your skills and experience is irrelevant.
Also, it would be nice if the employer provide adequate training of the job duties you are not familiar with, but they don’t have a legal obligation to do so.
(4) Changing your pay rate
An employer must pay the agreed upon rate for the work that you have already done or the hours that you have already worked. However, an employer is free to modify your pay rate for future work. In the absence of a contract, an employer is free to approach you and inform you that from tomorrow, your pay changes from x to y.
Standing behind your back (literally or figuratively) and watching your every move at work does not violate any laws. An employer is free to watch your work as closely and as often as they wish.
It’s not illegal for a manager to yell and even cuss at his subordinates. There is no legal obligation to be nice to employees or to treat them gently.