Celestina Mba was working at Brightwell Children's Home for three years and had never worked a Sunday because her employers accommodated her beliefs.
When her employers changed their policy, Mrs Mba attempted to reach a compromise by offering to work night or Saturday shifts, or accepting less pay, but they insisted she work on Sunday.
Mrs Mba has been told by an Employment Appeals Tribunal that her employer was justified in not accommodating her Christian observance of Sunday.
The Employment Appeals Tribunal held that Sunday was not a ‘core’ component of the Christian faith because some Christians would be prepared to work on a Sunday, and thus Christians as a whole do not need Sunday protected.
The Christian Legal Centre said the judgement was "very concerning" and "another example of the undermining of the Christian faith from the public square by the political and judicial elites".
Andrea Minichiello Williams, Chief Executive of the Christian Legal Centre, said: “As we reflect on Christmas, the Queen’s speech and a national census that continues to demonstrate our identity as a Christian nation, we may ask why our ruling elite seems ready to undermine all that most of us hold dear."
Mrs Williams said Christians who wish to observe the Sabbath may "be forced out of the workplace".
“In the past year we have seen mandatory tests of faith in relation to the wearing of crosses by Christians, belief about marriage between a man and a woman and now observing the Sabbath when in all cases reasonable accommodation could have been made," she said.
"Such tests do not appear to be similarly applied to Muslims who are permitted to wear the hijab and observe prayers and Sikhs with the kara bracelet.
“As the Government presses ahead with the redefinition of marriage perhaps the Courts will inform us what percentage of Christians need to believe marriage is between a man and woman before they will protect us?”