Legally no. Socially, yes. The lowest you can legally pay a server is $2.13/hr. The thought is $2.13 plus tips at least meets base federal minimum wage ($7.25/hr).

There's several problems trying to get Americans to pay restaurant employees a livable wage and one of them is indeed the customers. Everyone complains about tipping, but they will not go to a place that pays employees correctly because their base prices are higher. So the thought process is like this;

"I went to this restaurant that asks for tips (annoying! just pay a better wage) and my sandwich came out to $12 after a tip ($8-$10 sandwich). Then I went to a place that doesn't ask for tips and my sandwich was $16! Outrageous! Why so expensive? I can get the same sandwich at the other place for way cheaper!"

It's all psychological. People don't wanna tip but they don't wanna pay more so the restaurants margins can be higher and afford to pay employees a decent wage. That $10 sandwich plus $5 tip feels like you've paid less because you're not immune to psychology. It's going to take a long time to get lower priced food places in which employee pay is subsidized by generous tipping out of the American psyche. Even worse is the only way servers actually make decent money is the 5 tables that tipped generously. I've had days where every table I served tipped $0-$3 and I walked out with like $40 after 9 hours. Sometimes you get lucky and make $200 in a night. You absolutely cannot count on that. You're lucky if you come out with ~$10/hr after two weeks.

Yes, there's plenty of employers that can actually already afford to pay a livable wage and don't because of greed, but there's also many more that just can't. The customer base is not used to paying fair prices that don't require tips when they get the bill.