CHICAGO — When Tahera Ahmad logged on to Facebook late last week and posted a message about a troubling clash with a United Airlines flight attendant, she never expected the support that would pour in from people around the world, including the president of Northwestern University, where she serves as an interfaith chaplain.

Thousands of customers say they are boycotting United until its CEO, Jeff Smisik, apologizes for how Ahmad, a Muslim woman, was insulted by a flight attendant because she was wearing a headscarf.

United issued a statement Wednesday saying that employee, who worked for another airline that serves United, will no longer be allowed to serve United customers.

Meanwhile, the 31-year-old Morton Grove, Ill., native said the mass response to her complaint demonstrates the systemic problem of discrimination that has been allowed to go on for too long.

Ahmad was flying from Chicago to Washington, D.C., last week on a delayed United flight operated by Shuttle America when she said a flight attendant brought her an opened can of Diet Coke covered with a clear plastic cup.

When Ahmad requested an unopened can for sanitary reasons, the flight attendant declined, saying the airline didn’t serve unopened beverages, Ahmad said. When Ahmad pointed out another passenger’s unopened can, the flight attendant abruptly opened it, looked at Ahmad and said it was so she would not use that passenger’s can as a weapon. Ahmad accused the crew member of discriminating against her because she was wearing a headscarf.

Ahmad didn’t fly back to Chicago on United Airlines. She booked a flight on American Airlines, where the flight attendant served her an unopened can of Diet Coke – no questions asked.