"Tipping again changed in the 1960s, when Congress agreed that workers could receive a lower minimum wage if a portion of their salary came from tips. The minimum wage for tipped workers is $2.13, which has not changed in over 20 years, as long as those workers receive at least $7.25 in tips per hour. Saru Jayaraman, author of Behind the Kitchen Door, explains that a minimum wage of $2.13 means that their full wage will go toward taxes and forces tipped workers to live off their tips." [1]
[1] https://www.tripsavvy.com/a-brief-history-of-tipping-1329249