In his Easter Sunday sermon, O'Brien planned to address the cases of former nurse Shirley Chaplin and former British airways employee Nadia Eweida, Catholics whose employers told them they were not permitted to wear crosses in the workplace.
Both Chaplin and Eweida lost their discrimination suits in 2010, but intend to take their cases to the European Court of Human Rights. In ruling in Eweida's case, the judge said the matter was not one of discrimination, as Christians "generally" are not required to wear crosses as a tenet of their faith.
"In this light, I cannot but voice my concern at the increasing marginalization of religion, particularly Christianity, that is taking place in some quarters," reads O'Brien's sermon.
The BBC reported O'Brien, the leader of the Church of Scotland, was to deliver his sermon at Easter mass at St. Mary's Cathedral in Edinburgh.
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