Does anyone know what LABOR LAW i need to look up for wage earnings being withheld?

Because unless there is a union collective bargaining agreement in place, it would not be covered by labor law. At least in the US

Employers are free to use employees as needed, where needed, as they feel correct unless you can prove some EEOC guideline discrimination.

Edit: it's not going to be labor law. It's going to be a matter of reviewing your contract and having someone versed in labor law determine if the supervisor is in violation of award procedure for overtime and any job bidding requirements.

The issue of discrimination is valid legally only in government jobs. If you are in government job then this issue can be raised in Industrial Tribunal &/or labour court. But before approaching such authority you need to take up this issue with higher authorities highlighting the unjust and illegal action of the supervisor and offering yourself for the job which has been assigned to your junior superseding you.

There is no law covering this. It may be covered by your union contract though. You contact your union rep over the matter, it is handled by them, not law enforcement.

None. You are in a non union job that makes you an " at will " employee. They can ask anyone they want to

work overtime, or not. Happens at my place all the time.

There should be an entire section devoted to 'WAGES', holiday pay, long weekend pay, wages docked for reasons like unemployment insurance, etc.. Try googling it first as we do not know which state you live in and it varies from state to state.