Judges are to rule on a landmark case brought by four British Christians who claim to have suffered discrimination at work because of their faith.
British Airways employee Nadia Eweida, 60, and nurse Shirley Chaplin, 57, took their battle to the European Court of Human Rights after they were forced out of their jobs for wearing crosses in breach of company uniform codes.
A judgment will be handed down in relation to their cases and those of marriage counsellor Gary McFarlane, 51, who was sacked for saying he might object to offering sex therapy to homosexuals, and registrar Lillian Ladele, who was disciplined when she refused to conduct same-sex civil partnership ceremonies.
The four argue the actions of their employers contravened articles nine and 14 of the European Convention on Human Rights which prohibit religious discrimination and allow "freedom of thought, conscience and religion".
But lawyers for the Government, which contests the claim, argue their rights are only protected in private.
Campaigners on both sides believe the judgment is likely to shape future equality law in Britain.
Andrea Minichiello Williams, Director of the Christian Legal Centre, said: "These are landmark cases and we have waited a long time to get to this point. At stake is not only the future shape of Christian involvement in community life but the protection of important personal freedoms in a diverse society."
Keith Porteous Wood, executive director of the National Secular Society, said the case was likely to determine the future direction of equality law in Britain, and potentially in Europe. He said: "We believe any further accommodation of religious conscience in UK equality law would create a damaging hierarchy of rights, with religion at the top."
The four Christians have received public backing from Lord Carey, the former Archbishop of Canterbury.