Legal Question in Business Law in California

I'm not a tax expert and do not ordinarily respond to questions about taxatiion of income, but I have been an employer, met payrolls, and done the tax deduction calculations myself, so perhaps my thoughts will be of some use:

First, employers or their outside payroll services are not making decisions about how much to deduct and withhold from employee checks. They are using formulas and tables given to them every year for use during the following year by the IRS. I believe it is called Publication W.

Next, income on top of your base salary is, I think, taxed at the same rate, whether the employer (and employee) call it commission or bonus or overtime or whatever. Earned income is earned income.

Finally, withholding deductions are not determinations of the tax due; they are only estimates made pursuant to law. The employer is guided by information provided by you, the taxpayer, on your W-4, as well as the rules handed down by the IRS. The tax you actually owe and pay is determined by you (and the Internal Revenue Code, of course) when you prepare and file your 1040. If the employer is over-withholding you, that doesn't benefit the employer; it has to pass the withheld money along to the IRS. You can file a new W-4 if you are consistently getting tax refunds year after year due to over-withholding.