Four Indian nuns, teachers in California, were kept off an American Airlines flight after crew members complained of a sulfur smell in the cabin.

The passengers of flight number 631 were deplaned at Dallas, TX and a second security check was performed.

Even after that the nuns were not allowed in the plane as 'the captain felt uncomfortable' carrying them.

Hours later they were taken in another plane.

The incident took place on January 2.

"I felt discriminated and humiliated," Sr Tessy Pius, principal of Mary Immaculate Queen School in Lemoore, California, said. "It was really a bitter experience which I don't want to recount. Hope no one will have to go through what we went through," Sr. Pius, who hails from Cochin, in Kerala, said.

The four nuns, who teach at the elementary school run by the Diocese of Fresno, were returning to Lemoore after a Christmas visit to fellow Carmelite nuns in Wichita, Kansas on January 2.

Their tickets were for Fresno via Dallas. By noon they reached Dallas and boarded fight number 631. The plane began to move. But a few minutes later it stopped. The crew members came out and asked whether anybody smelt sulfur. "Some said yes and some said no. I did not feel anything, though one of the sisters with me said she smelt something," Sr. Pius said.

But the captain ordered everyone to deplane and go for a security check again. At the checking, everybody was cleared. But when the nuns reached the gate, the security woman asked them to wait in a corner. She began to question them. They showed the IDs and told her to call the bishop of Fresno, if she had doubts. She was very rude, Sr. Pius said. "We had all the proper legal papers. Three of us have Green Cards and one has work visa," she said.

Then they had the final call for the plane and it left without them.

They asked the security women why they were not allowed in the plane. She said the captain felt uncomfortable taking them.

Hours later they were taken in another plane to Los Angeles and then to Fresno. They reached the convent six hours later than scheduled.

The security people in Dallas said the nuns did not cooperate with the crew and also accused that they were sitting in wrong seats. "Both [charges] are not true. The plane was fully packed. We could not sit in other people's seats," Sr. Pius said.

Though bitter, they were not planning to complain. But Sr. Pius in her usual note to the parents of the students she tought just mentioned about this incident a few days later. The parents, most of whom whites, sent complaints to the airlines, officials and the media.

On January 26, the American Airlines sent a letter apologising for the incident. It also said they will be refunded $ 365 each they paid for the ticket.

When the incident happened, airlines were acting under strict security rules because the national threat level was orange, or high, American Airlines spokesman Tim Wagner told CNN.

Wagner would not reveal why the four nuns were held for additional screening, calling it "a matter of privacy." He said American Airlines captains have the final say over who flies on their planes.