A tip is money the guest chooses to leave. A service charge is set by the business and the guest has to pay it, so federal law treats it as the employer's revenue, not a tip (29 CFR 531.55).
If the employer passes some of it to you, that money is wages. It is taxed as wages and generally counts in your regular rate for overtime, but it cannot be used as tips for a tip credit.
Several states give workers more. In Massachusetts, a charge called a service charge or gratuity goes to the wait staff. New York presumes a charge for "service" is a gratuity unless guests are clearly told otherwise. Washington requires the receipt and menu to say how much goes to staff. See is a service charge a tip?
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