You are free to pay every employee whatever you can negotiate with that employee -- subject to the exception that you not discriminate against any employee based upon race, color, nationality, ancestry, religion, sex, sexual orientation, pregnancy, Equal Pay between sexes, age or disability.
In particular, were a male or female employee able to prove that you are paying a member of the opposite sex more money for the identical job description, that would violate the federal Equal Pay Act, which could expose you to liability for the pay differential, as well as punitive damages.
Other than that, your payroll negotiations with employees is unlimited.
Hope this helps.
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