People who come from mixed families often find themselves explaining and sometimes proving how they are related to their siblings, parents, or children. Recently, one mother found herself having to prove her relationship with her biracial one-year-old son at the Denver International Airport.

Lindsay Gottlieb, the coach of the women’s basketball team at Berkeley, shared her experience in a series of tweets. Gottlieb, a white woman, was with her husband when she was asked to show her son’s birth certificate to a Southwest Airlines employee. The couple had already presented the baby’s passport .

Chrissy Teigen chimed in to share her own experience, explaining that airlines may ask for proof in an effort to stop those attempting to traffic children.

According to the Washington Post, the airline has responded to the incident, claiming it’s a normal practice to “match the last names of a child and guardian” on U.S. flights. Others agreed with Teigen and the airline, pointing to the risk of illegal trafficking of children and the importance of safety over sensitivity.