[masukomi]

The federal minimum wage for servers and other tipped employees in the US is $2.13 per hour. I don't think it's increased in literally 40 years.

some restaurants have slow days, and the waitstaff doesn't have a choice. They get minimum wage because there are no tips, or there are so few customers as to make the tips meaningless vs the hours spent.

[RHSeeger]

However, as noted previously, that sub-minimum wage is "before tips". If, over the course of a week (iirc), the waiter makes less than the actual minimum wage ($7.25 federally), then the employer must make up the difference. That being said, I would guess any wait staff that go this route on a regular basis don't wind up employed for long.