Iraq's parliament has voted unanimously to bar the government from passing important reforms without its approval in an effort to curb Prime Minister Haider al-Abadi amid discontent over his leadership style, lawmakers said.

The chamber acted after Mr Abadi unilaterally enacted reforms in August that it deemed a violation of the constitution including his dismissal of the vice presidents and deputy prime ministers and cuts to salaries of government employees.

"Under this resolution no more absolute authorities for the prime minister," one member of parliament, who asked to remain anonymous, said.

Any rise in political tensions could undermine Baghdad's efforts to tackle an economic crisis and form a united front against Islamic State militants posing the worst threat to Iraq since a US-led invasion that toppled Saddam Hussein in 2003.

Last week over 60 members of Iraq's ruling State of Law coalition threatened to pull parliamentary support for Abadi's reforms - aimed at stamping out corruption and incompetence - if he did not heed their demands for wider consultation.

Many of the lawmakers who signed the letter are supporters of Mr Abadi's predecessor, Nour al-Maliki, whom critics branded as a polarising and authoritarian figure, allegations he denies.

Mr Abadi announced his reform campaign in August after popular protests gathered steam over graft and poor water and electricity services in Iraq, a leading OPEC oil producer.