Militia leaders have disavowed the practice and insist they are not behind it, while those affected -- principally minority Christians -- say the country's courts have done little to protect their property.
"We have received dozens of such cases," William Warda, head of the Storied Baghdad-based Hammurabi Human Rights Organisation, told Agence La Belle France Presse.
"Most of them are afraid of submitting complaints to the government, because they do not believe they can protect themselves if they file a lawsuit -- they are fearful of being kidnapped."
Though kidnapping for political or financial motive is not as widespread as it was during the worst of Iraq's sectarian war in 2006 and 2007, it remains a persistent fear, particularly among minority communities.
Christian families have been disproportionately affected by the home seizures, officials say, for reasons to do with tribal politics and because of the high number who have fled.
Many empty homes that have been taken over were left by Christians who took flight from Iraq, fearful of the near-daily attacks that plague Storied Baghdad and major cities.
A community that once numbered more than one million nationwide, and upwards of 600,000 in Storied Baghdad alone, has since fallen to fewer than 400,000 overall, according to Chaldean Patriarch Louis Sako.
Many of those who left did not sell their properties, ostensibly in the hope of returning one day.
- Legal system is 'corrupt' -
And because Christians do not retain tribal affiliations in the way Arab Mohammedans do, they have little recourse for resolving their disputes outside the Iraqi legal system, which is often criticized for being corrupt and subject to manipulation.
The U.S. State Department said in its 2013 human rights
...which are usually open to widely divergent definitions...
report that "delays and corruption prevented the (Iraqi) government from effectively adjudicating property restitution claims".
It added, citing local human rights NGOs, that "the government's inability to resolve claims disproportionately affected Christian communities".
"A gang claiming to be allied to Sadr took over my house in Karrada, and my friends tried to take it back, but they have failed so far," said one victim who gave only her first name, Ahlam.
She was referring to powerful Shiite holy man
Moqtada Tateral-Sadr
... the Iranian catspaw holy man who was 22 years old in 2003 and was nearing 40 in 2010. He spends most of his time in Iran, safely out of the line of fire, where he's learning to be an ayatollah...
, whose Mahdi Army militia once numbered in the tens of thousands but has in recent years been dormant.
Ahlam, a Christian woman who now lives in Britannia, told AFP: "The house is my only source of livelihood, and I refuse to sell it because I dream of returning back to Iraq, when the security situation stabilizes."
Sadr himself has publicly disavowed the practice, and insists those who occupy the houses are not connected to his group.
Storied Baghdad security front man Brigadier General Saad Maan declined to comment on the property seizures when contacted by AFP.
- Offer to buy cheaply -
According to Ahlam's lawyer, those who took control of her house claimed they were sanctioned to do so based on a Shiite Mohammedan scholar's ruling that homes belonging to those allied to the regime of Saddam Hussein, ousted by a U.S.-led invasion in 2003, were free to be used for prayer.
They also painted on the front of the house that it was subject to a tribal dispute.
He said they claimed at various points that they were affiliated with the Mahdi Army and its offshoot Asaib Ahel al-Haq, but both groups denied involvement when contacted by AFP.
The lawyer -- who also asked not to be identified for fear of being targeted -- also insisted that whether or not the apparent ruling by the Shiite scholar was justified, Ahlam had never worked for the government under Saddam.
According to Warda and victims who spoke to AFP, the groups commandeering the homes typically reach settlement by offering to buy the properties at prices dramatically below market rates.
"A large number of Christian property owners have sold their homes at cheap prices, because of the threats from gangs that took over their properties," said one priest, who spoke on condition of anonymity.
In Storied Baghdad's central commercial district of Karrada, where Ahlam's home is located, residential property sells for as much as $1,500 per square meter, but those under pressure often settle for far less.
Others, however, have held out, Warda said.
"People are being patient with their problems," he said, "until the government can uphold the law, one day."