Basketball coach says Southwest worker made her prove relationship to biracial son

Southwest Airlines is investigating an allegation that the University of California, Berkeley's head basketball coach for the women's team was stopped by ticketing personnel to "prove" her relationship to her 1-year-old son.

Lindsay Gottlieb, who was traveling with her son from Denver, Colorado, to Oakland, California, believes that the alleged incident began because she is white and her son is biracial.

Gottlieb, tweeting about her experience, wrote, "I'm appalled that after approx 50 times flying with my 1 year old son, ticket counter personnel told me I had to 'prove' that he was my son, despite having his passport. She said because we have different last name. My guess is because he was a different skin color."

Gottlieb continued on Twitter, saying that the ticketing employee asked her to produce a birth certificate, then asked her to show a Facebook post proving that she was the boy's mother.

In a statement to ABC News, Gottlieb said that though she had a passport verifying her son's age and both parents were present, the employee pushed her to further "prove" that he was her son, which she said "felt disrespectful and motivated by more than just concern for his well-being."

Gottlieb added, "While it was upsetting an emotional, I realize this was just one day of my life where I was uncomfortable and our family was made to feel 'less than' whereas others face similar situations on a daily basis. I hope the coverage this has received can serve as a learning opportunity and that all families -- regardless of how 'traditional' they may or may not look -- are treated with dignity and respect."

Southwest told ABC News that it is "looking into this specific interaction" and has "reached out to Ms. Gottlieb directly to address her concerns."

Gottlieb said on Twitter that the alleged incident was "demeaning and insensitive, not to mention inefficient." She added that the pair only made their flight because it was delayed and recommended better training for employees, and Southwest told ABC News that it plans to "utilize the situation as a coaching opportunity for" the employee.

Southwest also said that its "employees are well regarded for their hospitality" and that they always try to provide the best experience for anyone who chooses to travel with them but "when traveling domestically, FAA regulations require airlines to verify a lap child is under the age of 2 by reviewing a birth certificate or government-issued identification."

"Domestic travel does not require airlines to match the last name of a child and guardian," Southwest added.