Iraq’s parliament voted on Tuesday to reject a referendum on Kurdish independence planned for Sept. 25, authorizing the prime minister to “take all measures” to preserve Iraq’s unity, lawmakers said.

Kurdish lawmakers walked out of the session before the vote and issued statements afterwards rejecting the decision.

Western powers fear a plebiscite in Iraq’s semi-autonomous Kurdish region - including the oil city of Kirkuk - could ignite conflict with the central government in Baghdad and divert attention from the war against Islamic State militants.

“This referendum lacks a constitutional basis and thus it is considered unconstitutional,” the resolution said, without specifying what measures the central government should take to stop Kurdistan from breaking away.

Mohammed al-Karbouli, a Sunni Muslim lawmaker, said: “Kurdish lawmakers walked out of the session but the decision to reject the referendum was passed by a majority.”

A senior Kurdish official dismissed the vote as non-binding though an Iraqi lawmaker said it would be published in the official gazette after approval from the Iraqi presidency.

“The Kurdish parliament will definitely have a response to the resolution when it convenes on Thursday,” said Hoshiyar Zebari, former Iraqi foreign and finance minister and now a senior adviser to Kurdistan Regional Government (KRG) President Massoud Barzani.

Barzani had said he wants to pursue independence though dialogue without provoking a conflict.

A Kurdish delegation met officials in Baghdad for a first round of talks in August concerning the referendum. An Iraqi delegation was expected to visit the Kurdish capital of Erbil in early September for a second round of talks, but the visit has yet to happen with less than two weeks before the vote.

Iraqi lawmakers worry that the referendum will consolidate Kurdish control over several areas claimed by both the central government in Baghdad and the autonomous KRG in northern Iraq.

The KRG has said that it is up to the local councils of the disputed regions to decide whether to join the independence vote. Last month, Kirkuk voted to participate in the referendum, a move that stoked tensions with its Arab and Turkmen residents, as well as with Baghdad.

Kurdish peshmerga forces took control of the Kirkuk area and other areas claimed by Baghdad and the Kurds, after Islamic State militants overran around a third of Iraq in 2014 and Baghdad’s local forces disintegrated.

On Tuesday, Kurdish leader Barzani visited the city and said Kirkuk should have a “special status” within an independent Kurdistan, according to a tweet from his senior advisor Hemin Hawramy.

Iraq, Turkey, Iran and Syria oppose the idea of Iraqi Kurdish independence, fearing separatism could spread to their own Kurdish populations.

Kurds have sought an independent state since at least the end of World War One, when colonial powers divided up the Middle East and left Kurdish-populated territory split between the four countries.

Reporting by Ahmed Rasheed and Raya Jalabi; Writing by Ulf Laessing; Editing by Mark Trevelyan