Nadia Eweida, 55, said she decided to sue her employer for religious discrimination after having been suspended without pay for three weeks, Britain’s Daily Mail reported.
"I will not hide my belief in the Lord Jesus. British Airways permits Muslims to wear a headscarf, Sikhs to wear a turban and other faiths religious apparel," Ms Eweida said. "Only Christians are forbidden to express their faith."
Ms Eweida, a BA employee for seven years, works at its check-in counter at London's Heathrow Airport.
In a statement, BA said: "The case is ongoing, and is still under investigation, and as such it would be inappropriate to discuss it in detail. An appeal is due to be heard next week.
"British Airways does recognise that uniformed employees may wish to wear jewellery, including religious symbols. Our uniform policy states that these items can be worn underneath the uniform," it said.
"There is no ban. The rule applies for all jewellery and religious symbols on chains and is not specific to the Christian cross," it said. "Other religious items such as turbans, hijabs and bangles can be worn as it is not practical for staff to conceal them beneath their uniforms."
The newspaper said Ms Eweida, whose father is an Egyptian Coptic Christian and whose mother is English, was ordered last month by a manager at Heathrow to remove her cross or hide it beneath a company cravat.
She then asked for permission to wear the chain but was refused.
According to the newspaper, BA customer service manager Caroline Girling told Ms Eweida in a letter: "You have been sent home because you have failed to comply with a reasonable request.”