(CNN) United Airlines has apologized after a flight attendant's refusal to give an unopened can of soda to a Muslim passenger led to a social media firestorm.

The interaction on a flight operated by United partner Shuttle America left Tahera Ahmad in tears.

A Muslim chaplain and director of interfaith engagement at Northwestern University, Ahmad, 31, was traveling Friday from Chicago to Washington for a conference promoting dialogue between Israeli and Palestinian youths. She was wearing a headscarf, or hijab.

For hygienic reasons, she asked for an unopened can of Diet Coke, she said. The flight attendant told her that she could not give her one but then handed an unopened can of beer to a man seated nearby. Ahmad questioned the flight attendant.

"We are unauthorized to give unopened cans to people because they may use it as a weapon on the plane," she recalled the flight attendant telling her.

I am sitting on a United airlines flight in the air 30,000ft above and I am in tears of humiliation from discrimination.... Posted by Tahera Ahmad on Friday, May 29, 2015

United spokesman Charles Hobart said that a flight attendant had tried several times to accommodate Ahmad's beverage request but that there was a "misunderstanding."

Hobart did not elaborate on the so-called misunderstanding but said United officials spoke to the chaplain Saturday afternoon to "get a better understanding" of what happened and to apologize for "for not delivering the service our customers expect when traveling with us."

United offered an apology to Ahmad on Wednesday.

"Ms. Ahmad was our customer and we apologize to her for what occurred on the flight," United said in a press release

"After investigating this matter, United has ensured that the flight attendant, a Shuttle America employee, will no longer serve United customers."

The incident happened on a Shuttle America flight that feeds United. Bob Birge, spokesman for Shuttle America's parent company, Republic Airways Holdings, said Monday that Republic beverage policy doesn't prohibit serving unopened cans to passengers.

"There is policy and procedure for the beverage service, and there is no differentiation between opened and unopened cans," he said. "When a passenger requests a full can of soda, it must first be determined that enough quantity exists to provide beverage service throughout the cabin. I don't believe that was the case here, as the passenger was offered a full can of soda."

When asked about the "weapon" comment, Birge said, "I am unaware of an aviation incident involving a can of soda that was ever used" in that manner.

On Facebook, Ahmad wrote that she was "truly disappointed" with the airline's response, which she said "disregarded and trivialized" the discrimination she experienced.

"I have not received a written sincere apology for the pain and hurt I experienced as a result of the discrimination and hateful words towards me," she wrote at the time. "This is not about a can of soda."

Ahmad, who has Premier frequent-flier status with the airline, wrote that she been served unopened beverages on previous United flights and that she did not want the flight attendant fired.

"I simply did not expect United Airlines to dismiss the unwarranted and unfortunate rude behavior, discrimination and hateful words but rather acknowledge their accountability and role in the painful experience," she wrote.

Ahmad said that when she told the flight attendant she felt she was being discriminated against, the attendant abruptly opened the beer can of the man seated near her.

"It's so you don't use it as a weapon," Ahmad said she was told.

Shocked, Ahmad asked other passengers if they had seen what happened.

A man sitting across the aisle turned to her and yelled, "You Muslim, you need to shut the f*** up," she said.

"What?"

The man leaned over, according to Ahmad, and looked her in the eyes.

She said that the man told her: "Yes, you know you would use it as a weapon. So shut the f*** up."

"I felt the hate in his voice and his raging eyes," Ahmad wrote in an earlier Facebook while the plane was still in flight. "I can't help but cry ... because I thought people would defend me and say something. Some people just shook their heads in dismay."

After her initial post, people took to social media in to support, using the #unitedfortahera hashtag. Some pledged to boycott United.

Suhaib Webb, a prominent Muslim American imam, tweeted, "I'm asking all of you to let @united know that you are disgusted with this bigotry." He also tweeted a photo of a can of Diet Coke over #unitedfortahera.

In an earlier statement, Hobart said the airline "strongly supports diversity and inclusion."

"We and our partners do not discriminate against our employees or customers," the statement said. "We are also discussing the matter that Ms. Ahmad describes with Shuttle America, our regional partner that operated the flight."

Ahmad said her intent is not going after the airline.

"This is about bigotry and racism and our country is going through a very difficult time right now. Dr. Martin Luther King Jr. and so many others worked so hard ..." she said, breaking into tears.

"They strove so hard so that Americans would not mistreat each other on the basis of the color of their skin or religious or ethnic background but I guess we're still on that journey."

The flight attendant as well as the pilot later apologized, she said.

"She said she's working on her rude behavior and that the man (sitting across the aisle) should not have said anything," Ahmad recalled.

Ahmad was recognized at the White House last year "as a leading Muslim female in the United States" during Women's History Month, according to Northwestern University. She had previously attended a Ramadan dinner hosted by President Barack Obama.

In 2013, Ahmad sparked outrage among Islamic conservatives when she became the first woman to recite the Quran at the Islamic Society of North America convention in Washington, the nation's largest Muslim gathering, according to Northwestern.

Ahmad was born in India and grew up in Morton Grove, Illinois. She said she has been spat on and had her hijab ripped off in Islamophobic encounters after the September 11, 2001, attacks.

"This time I was being treated as a threat to everyone around me 30,000 feet above the ground and being told that I could use a can of Diet Coke as a weapon," she said. "And no one said anything."

The incident comes amid growing hostility toward Muslims living in the United States.

On Friday, protesters at a "Freedom of Speech" rally outside a Arizona mosque were met by counterprotesters. The two groups lined opposite sides of the street in front of the Islamic Community Center of Phoenix. They yelled at each other as a line of police officers kept them apart, CNN affiliate KNXV reported.

The Islamic center is the mosque once attended by Elton Simpson and Nadir Soofi , who drove from Arizona to a Dallas suburb to shoot up a Prophet Mohammed cartoon contest there. Both were killed by police this month. Many Muslims consider demeaning depictions of Mohammed to be blasphemous and banned by Islamic law.

In Washington, activist and conservative blogger Pamela Geller of New York wanted to place ads showing cartoons of Mohammed in the capital's transit system. She hoped to display the winning cartoon from her group's contest in Texas, the one where Simpson and Soofi were killed by police. The Washington Metro board voted to stop showing issue-oriented ads throughout its system.

Events such as this have some Muslims scared, said Imraan Siddiqi with the Council on American-Islamic Relations.

"Recently, the mosques here in Phoenix actually received threatening letters -- very specific threats, saying that we are going to massacre your congregations," he said.

In a national survey by the Pew Research Center in 2013 , 42% of respondents said Islam was more likely than other religions to encourage violence among its believers. In addition, Muslim-Americans are seen as facing more discrimination than other groups, including gays and lesbians, Hispanics, African-Americans and women.

In the same survey, 45% of the respondents said Muslim-Americans face "a lot" of discrimination, and 28% said Muslims are subject to some discrimination.

United said Wednesday that it doesn't tolerate discrimination on its flights and that the company will keep educating its staff on proper protocol.

"Customer-facing employees for Shuttle America also undergo cultural sensitivity training, and United will continue to work with all of our partners to deliver service that reflects United's commitment to cultural awareness."