Christians in Mosul, Iraq’s second-largest city, are facing an ultimatum: convert to Islam, pay a tax or abandon everything and leave.

If they don’t, they could be killed.

in this Monday, June 30, 2014 photo, militants from the al-Qaida-inspired Islamic State of Iraq and the Levant (ISIL) celebrate the group’s declaration of an Islamic state, in Fallujah, 40 miles (65 kilometers) west of Baghdad, Iraq. (AP Photo)

The ultimatum was issued by the Islamic State of Syria and Iraq (ISIS), the militant group that overran Mosul last monthAl Jazeera reported Friday.

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The Sunni rebel group issued the orders in a letter after Friday prayers. The document, obtained by Al Jazeera, states that the order was issued after Christian leaders failed to attend a meeting called by the group.

In response, the group says in the letter that Christians must either convert to Islam, pay a tax on non-Muslims known as jiziya, or give up their posessions and leave the city. Failure to do so would result in a death penalty, “as a last resort”.

TheBlaze has previously reported on ISIS’ plans to impose on Christians a “jizya,” a fine more like protection money than a tax.

A displaced Iraqi Christian girl who fled with her parents from the Christian village of Hamdania near Mosul province in Iraq, plays by a balloon at a temporary shelter for the displaced Christian families in Ainkawa, a suburb of Irbil, with a majority Christian population, Iraq, Saturday, June 28, 2014. Around 2,000 Christians had entered the Kurdish city of Irbil by Thursday morning, June 26. A Christian official there said the Kurdish region is the only part of Iraq where Christians are protected from violence. (AP Photo/Hussein Malla)

Iraq’s Christian population has been shrinking ever since the U.S. invasion in 2003, and many Christians have fled the ISIS rampage across northern Iraq.

Ignatius Joseph III Younan, Patriarch of Antioch of the Syriac Catholics, leaves a church where displaced Iraqi Christian families, who fled the village of Hamdaniya near Mosul, had taken refuge, in Irbil, Iraq, Sunday, June 29, 2014. (AP Photo/Hussein Malla)

Al Jazeera reported that Mosul’s Christian population stood at roughly 3,000 before ISIS took over — it’s unclear how many Christians remain in the city now, especially considering as many as one-third of the city’s residents fled as ISIS invaded.

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