15 Turkish churches are receiving death threats for denying Allah, according to World Watch Monitor.
The leadership and congregations of 15 protestant churches in Turkey have been sent death threats since 27 August.
The Association of Protestant Christians in Turkey believes it is likely that the threats come from one source.
"Threats are not anything new for the Protestant community who live in this country and want to raise their children here," they said earlier this month. "But with the recent increase in systematic threats, from this country's west to east and north to south, in different cities, we think that these messages, coming close together and resembling each other, are coming from the same source."
Most of the Christians being attacked used to be Muslim and the threats vow to kill, massacre and behead apostates.
They are accused of having "chosen the path that denies Allah" and "dragged others into believing as you do... As heretics you have increased your number with ignorant followers."
Turkey is rare amongst Muslim-majority nations in that its citizens are free to change their religious identity legally.
World Watch Monitor reported saw a copy of one message. It showed the IS flag and named itself "those who go to jihad" warning "Perverted infidels, the time that we will strike your necks is soon. May Allah receive the glory and the praise."
The messages often quote Al-Ahzab, the chapter of the Quran which threatens "those who spread false news... Accursed, they shall be seized wherever found and killed with a horrible slaughter."
They are also circulating a Youtube video entitled "The religious proofs why apostates should be killed."
The Association is encouraging churches who receives such threats to report them.
This was sourced from World Watch Monitor.
