Five Iraqi MPs have announced a boycott of cabinet meetings, deepening the political crisis and leaving the unity government without any Sunni members.
Mr Maliki's administration is looking more fragile than ever
The ministers, who are loyal to former Prime Minister Ayad Allawi, blamed what they said was the Shia-led government's failure to end sectarian favouritism.
The Iraqi National List ministers included Sunnis, Shia and a Christian.
Iraq's largest Sunni-Arab bloc, the Accordance Front, withdrew six ministers from the cabinet last week.
So far this year, 17 government ministers - nearly half of the cabinet - have either suspended their participation or quit.
The BBC's Andy Gallacher in Baghdad says it is a serious setback for any attempts at reconciliation between Shia and Sunni factions.
Our correspondent says the latest events leave the administration of Prime Minister Nouri Maliki looking more fragile than ever.
Iraqi MPs are not due to return to parliament until early September when their holidays end.