Lindsay Gottlieb, the coach of the women’s basketball team at the University of California, Berkeley, was at the Denver International Airport with her biracial 1-year-old son when she was asked by a Southwest Airlines employee to “prove” that she was the child’s mother, The Washington Post reported. Gottlieb, who was with her husband, said she was asked to present the child’s birth certificate after the employee reviewed his passport, citing “federal law.” The employee also asked Gottlieb to present a Facebook post with the child for further proof, because the child has a different last name. Gottlieb, who is white, wrote on Twitter that “[m]y guess is because he has a different skin color.” She also wrote that she has flown “approx 50 times” with her son and had no issues up until now. Southwest Airlines apologized for the interaction, and noted that it was the company’s policy to check birth certificates to ensure “lap children” are younger than two years of age. The airline said that it was not normal practice to “match the last names of a child and guardian” on U.S. flights. “We are fine. It was wild, but, I fear, much more common for people that don’t look like me,” Gottlieb wrote on Twitter.