Last week, Dikmen Onat, the head of the education union Egitim-Sen for the province of Denizli spoke out at the distribution of the book to students, saying that its contents called for children to centre their lives around the mosque.
Officials have launched an investigation into the distribution of the book, entitled Namaz; pole of religion which called on children to have a mosques based life.
The books were handed out by the deputy principal of a boarding school in Denizli on the anniversary of the birth of prophet Mohamed.
Onat said on Monday he had been receiving threats over the phone and would apply to the Ankara Chief Prosecutor to investigate the threats.
We are being accused because we are supporting the republic, Onat said.