"Sangma has lost majority. We want a change of leadership and immediate holding of Congress Legislature Party meeting to elect a new chief minister," Rural Development Minister F W Momin said.
Fifteen rebel MLAs are now camping in Delhi to meet the Congress high command to apprise the political development in the hill state while three will arrive soon, he said.
Momin claimed that six of the nine ministers of the Mukul Sangma government, including Deputy Chief Minister Rowel Lyngdoh, have lost confidence in the chief minister and want a change of leadership.
MLA and political advisor to the chief minister Sayeedullah Nongrum said a memorandum, signed by all 18 rebel MLAs, has been submitted to Congress chief Sonia Gandhi urging her to replace Sangma.
"Sangma's style of functioning is totally autocratic, vindicative and he has been involved in rampant corruption besides hobnobbing with the insurgents," Nongrum alleged.
Sangma sworn in as chief minister on April 20, 2010, after 21 of the 28 Congress legislators revolted against then chief minister D D Lapang.