A Free Presbyterian minister has branded a book which promotes humanism in primary schools as "exploitation" of young minds.
Rev David McIlveen said there should be a "clear barrier" between the message of humanism and young children.
His comments come after Northern Ireland Humanists revealed it has been sending out free copies of the book, What is Humanism? to primary and secondary schools across the province.
The non-fiction children's book by authors Michael Rosen and Annemarie Young explores humanist views of morality and ethics and the relationship between religion and the state.
The books are being delivered to upper primary and lower secondary pupils following a crowdfunding campaign.
Northern Ireland Humanists, part of the British Humanist Association (BHA) charity, represent non-religious people in Northern Ireland.
The book also features content provided by broadcaster Stephen Fry, writer and broadcaster Natalie Haynes, and best-selling author Philip Pullman, who are all patrons of the BHA.
Rev McIlveen, who has retired from Sandown Free Presbyterian Church in east Belfast, said that while it's important not to censor literature, there is also a right to challenge the contents of the book.
"We know that humanism is basically anti-God and therefore anti-Christian," he said. "I think to advocate humanism can't go unchallenged and I think it is important that people do have the opportunity to challenge that and I would appeal to Christian parents particularly to express a very strong and vocal opposition to the message of humanism.
"I feel that for a child of primary school age, humanism is not something that should be put into their mind.
"I think that they are far too young to even make that decision as to the rights and wrongs of humanism and I think this is an exploitation of young people to try and indoctrinate them into a view that many people in Northern Ireland would reject.
"I would feel very strongly about the fact there should be a clear barrier between the message of humanism and impressionable minds."
Northern Ireland Humanists trains and accredits celebrants here who non-religious humanist weddings, funerals, and naming ceremonies. It also provides trained pastoral carers in hospitals and prisons, alongside school speakers who can help teachers with delivering lessons on humanism.
Northern Ireland Humanists coordinator Boyd Sleator said the local religious curriculum is "dominated" by the Christian religions.
"It's important that schoolchildren also have the opportunity to reflect widely on the different beliefs and values that make up our society and the world we live in today," he said.
"Michael Rosen and Annemarie Young have created an excellent introduction to humanism, which is the name given to those rational, non-religious, ethical values which thousands of people across Northern Ireland rely on every day.
"Children across Northern Ireland now have a resource designed with them in mind so they can improve their understanding of humanism."