A mother from California said she was “appalled” when a Southwest Airlines employee asked her to “prove” that she was the mother of her biracial son, even after providing the boy’s passport.

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Lindsay Gottlieb coaches the University of California at Berkeley's women's basketball team. She was flying from Denver to Oakland with her 1-year-old son Monday when an employee at the Southwest ticket counter asked to see her son's birth certificate, Gottlieb tweeted.

"My guess is because he has a different skin color," Gottlieb said.

"We had a passport that verified our son's age and identity, and both parents were present," Gottlieb said in a statement to The Washington Post. "But still being pushed further to 'prove' that he was my son felt disrespectful and motivated by more than just concern for his well-being."

California women's basketball coach Lindsay Gottlieb claimed an airline employee stopped her from boarding because the worker didn't believe her 1-year-old biracial son was hers. Southwest Airlines has issued an apology.

Credit: Marcio Jose Sanchez

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Credit: Marcio Jose Sanchez

Gottlieb tweeted that the employee asked for documented proof of her relationship to her son because they have different last names.

She also said that another mother traveling through the airport with her child was not asked for extra documentation, even though they also have different last names.

"Not shockingly, not a mixed race fam," Gottlieb tweeted.

She added that she has traveled with her son “over 50 times” before and this discussion almost made them miss their flight.

According to The Washington Post, Southwest Airlines officials reached out to Gottlieb to address her concerns and apologized if "our interaction made this family uncomfortable."

Airline officials added that it is airline policy to verify a child’s birth certificate or passport if they are under the age of 2, but employees aren’t required to match the names of a guardian and child for domestic flights.

Gottlieb said she hopes this brings awareness to others about respecting “non-traditional” families.