The planned plenary session of the People's Consultative Assembly (MPR) to amend the 1945 Constitution is under threat after the Golkar Party withdrew its support for the amendment, decreasing the number of amendment proponents to well below the required threshold.

Golkar followed the Democratic Party (PD), which earlier retracted its support for unspecified reasons for an amendment to Article 22 (d) of the Constitution to empower the Regional Representatives Council (DPD). Eleven Golkar lawmakers originally gave their support to the DPD-proposed amendment.

Golkar figures were unavailable for comment on the political reasons behind the retraction, which came only one day after the MPR announced its plan to hold the plenary session.

The MPR is a joint sitting of both the DPD and the House of Representatives. The House has 550 legislators while the DPD has 128 representatives.

The chairman of the Golkar Party faction at the MPR, Hajriyanto Tohari, confirmed his party's decision to allow more time for further analysis of the proposed amendment and its political consequences.

"It is not the right time to amend the Constitution, since it has been amended four times between 1999 and 2002," he said, adding that he would deliver a formal retraction to the MPR's leadership Wednesday.

With the withdrawal of Golkar's political support, the number of amendment proponents drops from 234 to 223. The Constitution requires at least 226 supporters before the MPR can hold a plenary session to amend the constitution.

Regional representatives said they are optimistic of winning more support from lawmakers to allow the plenary session to be held later this year in September.

The Indonesian Democratic Party of Struggle opposed the proposed amendment on the insistence that a bicameral legislative system is not recognized by the Constitution.