Iraq's federal court ruled on Monday that Prime Minister Haider al-Abadi's move to abolish the largely ceremonial posts of the country's vice president and deputy prime minister is unconstitutional.

Under Iraq's constitution, abolishing the posts would require the approval of an absolute majority in parliament followed by a national referendum, the court said in a statement.

The decision, which is binding for the Iraqi government, was a slap for al-Abadi, who canceled the posts last year as part of a wide-ranging reform plan that was approved by his Cabinet and passed by Parliament. It was intended to shore up public support for his government in the face of widespread protests.

The cancellations were also an apparent attempt to consolidate power under al-Abadi's government in order to combat corruption and tackle the country's ballooning budget crisis, sparked in part because of a plunge in the price of oil over the past two years, government spokesman Saad al-Hadithi said.

"The return of the (vice president and the deputy prime minister) will affect the expenses of the state," al-Hadithi said.

The decision underscores the government's enduring weakness as Iraqi forces prepare to retake the city of Mosul from the Islamic State group. While the U.S.-led coalition has closely supported Iraq's security forces in the military fight against IS, coalition officials say the Iraqi government is responsible for enacting political reforms that will prevent IS from growing in power in Iraq once again.