Celebrity tattoo artist John Petro reportedly allowed Jenner, 16, to place her gloved hands on top of his as he administered Richie's tattoo.
Witnessing the event were Jenner's half-sister Khloe Kardashian, as well as their friends French Montana and Mally Mall.
The Los Angeles County Department of Public Health said only people 18 and older can legally participate in the process of administering a tattoo. Should authorities pursue the matter, Jenner could be charged with a misdemeanor and fined, while Petro could have his license suspended.
Celebrity Families of 2014 [PHOTOS]