The interim Iraqi government has ordered the party of former exile and anti-Saddam Hussein activist Ahmed Chalabi to leave its Baghdad HQ.
Ahmed Chalabi was once tipped to replace Saddam Hussein
The Iraqi National Congress was given 24 hours to vacate its offices, which used to house the intelligence services.
A government spokesman said more orders would follow against parties that had seized state property.
The INC said the order was part of a continuing conspiracy against it.
A host of other Iraqi parties occupy buildings and property that housed security and government offices before the fall of Saddam Hussein.
In recent days, arrest warrants have been issued accusing Mr Chalabi of counterfeiting and his nephew Salem - head of the tribunal trying Saddam - of murder.
Both men, who are currently abroad, deny the charges.
Ahmed Chalabi developed close ties with the Pentagon and Washington hawks during his long years in exile from the Saddam Hussein regime.
Their relationship has since deteriorated.
Privately, senior US officials accuse their former protege of misleading them about the former Iraqi ruler's alleged weapons of mass destruction - intelligence on which Washington based its case for war.
Mr Chalabi is also accused of passing sensitive intelligence to neighbouring Iran.
Salem Chalabi, who is head of the tribunal trying Saddam Hussein, says he is the victim of a smear campaign.
Speaking in London on Monday, he said he feared for his life and wanted assurances about his safety before returning to Iraq.
"My life is daily threatened because of what I'm doing... there is some element of a smear campaign against me and therefore against the tribunal," Salem Chalabi told BBC Radio 4's Today programme.
He said he was in talks with Iraq's President Ghazi Yawer and Prime Minister Iyad Allawi to negotiate his return.