Derry, UK - A teachers' union has urged the board of governors at a Londonderry grammar school to resign after it decided to introduce its own entrance examination.
Lumen Christi College is to bring in its own form of academic selection when the 11-plus is abolished this year.
The Catholic Bishop of Derry, Dr Seamus Hegarty, a senior trustee of the college, criticised the move.
The Irish National Teachers' Organisation called on the board to "do the honourable thing" and step down.
Brendan Harron of INTO said: "Much has been made in recent years of the importance of the 'ethos' in Catholic schools, which is allegedly based on the gospel values of Jesus Christ.
"Yet we here have the governors of such a school taking a decision to perpetuate the most unfair, immoral and socially divisive system of separating children into those who will have opportunity and those who will not. "
Bishop Hegarty said he was opposed to the aptitude test because academic selection did not offer an equal opportunity to all.
"As senior trustee, I had no knowledge of their (the board of governors') decision and became aware of it through the media. I cannot support this decision," he said.
He said he had been supporting the efforts of local Catholic post-primary schools to work out an alternative to academic selection based on equal opportunity.
Education Minister Caitríona Ruane said she agreed with Dr Hegarty, adding that the Department of Education would not fund or support any such entrance exam.
"Schools considering a breakaway entrance exam should also be aware of the considerable legal and financial risks they may face if they decide to proceed," she said.
"There is the potential for multiple appeals and litigation aimed at overturning admissions decisions."