Bush was scheduled to meet with Prime Minister Nouri al-Maliki on Wednesday and Thursday in Amman, the Jordanian capital. The al-Sadr bloc in parliament and government is the backbone of al-Maliki's political support, and its withdrawal, if only temporarily, would be a severe blow to the prime minister's already shaky hold on power.
"If the security situation and services don't improve, and if Mr. prime minister does not cancel his meeting with Bush the criminal in Jordan, we will suspend our membership at the Council of Deputies (parliament) and government," Qusai Abdul-Wahab, an al-Sadr follower, said.
The politicians said U.S. forces were to blame for Thursday's bombings in Sadr City that killed more than 200 people because they failed to provide security.
"We say occupation forces are fully responsible for these acts, and we call for the withdrawal of occupation forces or setting a timetable for their withdrawal," Abdul-Wahab said.
Al-Sadr's followers hold six Cabinet seats and have 30 members in the 275-member parliament.