Hello. My question is, is it legal for a company to deny you your 90 day raise on the theory that they want to see if your going to stay with the company?

Unless you are represented by a labor union, and a 90-day wage increase is
Part of the union contract, or there is a signed agreement between you and
The employer, stating specifically that this increase in pay will go into effect
After 90-days, such an increase, or any increase at all so long as the salary meets
Minimum wage requirements, is at the discretion of the employer.