The Government will change the law if necessary to make sure employees can wear religious symbols at work, Prime Minister David Cameron said.
Nadia Eweida is taking her case to the European Court of Human Rights in September after she was sent home from work for wearing a crucifix in what backbench Tory MP David Davis described as a "disgraceful piece of political correctness".
He said he was surprised the Government was resisting Ms Eweida's appeal, telling Mr Cameron he could not believe it would support religious suppression in the workplace.
In reply, Mr Cameron said he fully supported the right of people to wear religious symbols at work. He said: "I think it is an absolutely vital freedom."
Mr Cameron added: "What we will do is that if it turns out that the law has the intention (of banning the display of religious symbols in the workplace), as has come out in this case, then we will change the law and make clear that people can wear religious symbols at work."
Miss Eweida, 59, a Pentecostal Christian of Twickenham, south-west London, received widespread publicity when she was sent home in 2006 after refusing to remove a necklace with a cross or hide it from sight. An employment tribunal ruled Ms Eweida had not suffered religious discrimination, but the airline changed its uniform policy after the case to allow all religious symbols, including crosses.
In a separate case, nurse Shirley Chaplin was moved to a paperwork role by the Royal Devon and Exeter NHS Trust Hospital after refusing to remove a necklace bearing a crucifix.
Mr Davis said the Government needed to support religious expression in the workplace.
In his question to Mr Cameron, he said: "On September 4, the European Court of Human Rights is hearing the case of Miss Nadia Eweida, the lady who lost her job at British Airways for wearing a crucifix as a mark of her Christianity. The behaviour of British Airways in this was a disgraceful piece of political correctness, so I was surprised to see the Government is resisting Miss Eweida's appeal."
Mr Cameron joked that he did not always agree with Mr Davis, one of his rivals in the 2005 leadership election for the Tory Party, but said he "wholeheartedly agreed" with him on this case.