An author is suing the family of captive Israeli soldier Gilad Shalit, saying he plagiarised one of her books.
When the Shark and the Fish First Met, written by Gilad Shalit when he was 11, was published in 2008, acknowledging it was "inspired" by Shelly Elkayam.
But she says it is her story and she should be entitled to royalties.
The tale of two enemies that choose to live in peace has been used to publicise the cause of Sgt Shalit, who Hamas have held for nearly four years.
Ms Elkayam told Israel radio Sgt Shalit's story had only superficial changes from her book, When the Snake and the Mouse First Met.
"I love Gilad Shalit and want him to return alive and healthy," she said.
But she added, "I'm a student, I'm a mother making a living for her son... Just like it's his right to be free, it's my right that my rights will be protected... I'm a literary hostage," she added.
Sgt Shalit's father Noam said he and his wife had been unaware of the story until it was produced by Sgt Shalit's former teacher after his capture.
He said they had been careful to acknowledge the probable inspiration from Shelly Elkayam "even though we didn't have any confirmation, because we haven't had any contact with Gilad for years," he said.
When the Shark and the Fish First met was published in 2008, with illustrations by members of the Israeli Illustrators' Association.
It currently sells for $15 to $19 in Israel. Mr Shalit said there was "not a lot of money" raised from the book, but all of it went to help fund the campaign for his son's release.
The story has been translated in pamphlet form from Hebrew into Russian, French, Italian, Arabic and English.
In Sgt Shalit's version, a shark and a fish meet in the sea, and play hide and seek together.
But when they return home separately to their mothers, they are both told not to play together, as the shark is a natural predator of the fish.
Years later they meet again, play together in secret, and eventually confront their mothers together "and from that same day the sharks and the fish live in peace", the story ends.
Sgt Shalit, 23, was captured in a raid into southern Israel by Palestinian militants from Gaza, in 2006.
Hamas want hundreds of Palestinians held by Israel, including senior militant leaders that Israel holds responsible for the deaths of dozens of Israeli citizens, to be freed in exchange for Sgt Shalit's release.
Israel holds about 10,000 Palestinian prisoners in jail on security grounds - a major bone of contention with the Palestinians.
Hamas released a video last year showing Sgt Shalit, apparently in reasonable physical health.