Food service workers are required to make at least minimum wage in the United States. Most of them are paid $2.13 minimum per hour but then must claim their tips to their employer. The employer is supposed
to check that when tips are added into the hourly salary that the server has earned minimum wage for the area (since some states and cities have increased minimum wage). If minimum wage is not made when tips are added to the hourly salary, the restaurant or other place is to make up the difference. The calculations are made on a per pay period basis, and tipped employees are also subject to overtime rules and other labor rules regarding breaks etc. So - when you go to a buffet or something, know that the employer is supposed
to ensure that all staff is being paid at least minimum wage.
BTW: I used the italic emphasis because I know that many employers and employees are not good about following the law on this one. Some employees will not report all of their tips since they have to pay taxes on it, and many employers will not do the calculations and pay rises to ensure that the employee is making minimum wage since they have to pay social security taxes on it. Employers are allowed to calculate what tips should be for servers to mitigate under reporting problems, but that amount is 8% of gross receipts. Also, the service fee for large parties isn't necessarily considered a tip for tax purposes so the restaurant might be retaining it and not passing the amount onto the server. For many service workers, pay law compliance becomes a YMMV situation. In fact, a story that recently came out showed an employer forcing employees to pay them to work there. https://www.dol.gov/newsroom/releases/20160216-4
As noted by the department of labor, the issue is that many employees are not aware of the laws regarding minimum wage and are also not aware that they can file a claim with the Department of Labor for violations of the Fair Labor Standards Act.
Due to various restaurants non-compliance with the law, it is hard to know if the employee is getting paid fairly and is considered a tipped employee or not. Places like Noodles Etc. when they make their policies clear are very helpful to consumers in understanding if labor laws are being upheld.