With the federal minimum wage for tipped workers set at $2.13 an hour, many workers in service jobs such as waiters, hairdressers and bartenders lean heavily on tips to subsidize their income. Even with tips, they still may not reach the standard minimum wage of $7.25, in which case employers are required to step in and make up the difference, accoriding to the Fair Labor Standards Act.

Tipping in the service industry has recently come into focus with the "No Tax on Tips" — a provision baked into the GOP spending bill that would remove federal taxes from tips for workers who earn less than $160,000. 

If passed, "No Tax on Tips" could offer relief to the 4 million people in the U.S. who work in tipped occupations, about 2.5% of all U.S. workers, according to the Yale Budget Lab.