Earlier in the year CS Lewis publisher HarperCollins signed an agreement with the CS Lewis Company making them the primary publisher of Lewis's works.
HarperCollins has since developed plans to write new books based on the existing titles, which have already sold more than 65 million copies worldwide.
Prominent writers including novelist Piers Paul Read and CS Lewis biographer AN Wilson are among those who have denounced the plans.
"They're turning Narnia into a British version of Mickey Mouse," John G West, co-editor of The CS Lewis Readers Encyclopaedia told the New York Times.
"What they've figured out is that Harry Potter is a cash cow. And here's a way they can decompartmentalise the children's novels from the rest of Lewis."
Academics are most angry at reports that religious references will be removed.
Lewis was inspired by religious themes throughout his work. The Narnia stories are an allegory of the life of Christ.
In the books, the character of Aslan, an inspiring lion, represents Christ, who is persecuted but eventually triumphs.
"I think it (rewriting the books) is an appalling idea," Brian Sibley, CS Lewis biographer and author of A Treasury of Narnia, told BBC News Online.
"Lewis wrote the books by his own admission to show people what he believed in," he said.
"That's what the books were about and taking this out leaves the books as much less than they really are."
Lewis wrote the series with a clear ending - at the end of The Last Battle everybody is dead and living happily in an afterlife - so writing a sequel would be extremely difficult, said Mr Sibley.
He added he was not opposed in principle to the idea of new adventures based on the Narnia characters, but asked: "Who would be up to writing them?"
The Lewis estate has denied that the rewriting plan is part of a calculated move to reshape the author's image.
A HarperCollins spokesman said the reason for the new books was to capture a broader audience.
Whatever happens, the company insists it will continue to publish the unaltered original works.
Clive Staples Lewis was born in Belfast and became a professor of Medieval and Renaissance English at Oxford, where his circle included JRR Tolkien.
The Lion, the Witch and the Wardrobe was first published in 1950, before the six other Narnia books.
It was chosen as the most influential children's book of the 20th Century last year by parents, teachers and librarians.
It has been adapted many times for the stage, television and radio.