Brar, a senior leader from Punjab, had recently criticised the functioning of the party and had suggested that Congress President Sonia Gandhi and Vice President Rahul Gandhi should take a break for some time and hand over the reins of the party to somebody else.
Singh, who revolted against Haryana Chief Miniser Minister Bhupinder Singh Hooda had met BJP chief Amit Shah last month and appears set to dump the party and join BJP.
Singh was dropped as a member of the party's apex decision making body Congress Working Committee on July 31, when the party also slapped a showcause notice to him pointing to media reports that he is "hobnobbing" with BJP leaders.
Brar was slapped a notice by the state unit of Punjab. Their issues were referred to the Central Disciplinary Committee after reports from the respective AICC general secretary in-charges of their states.
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"The disciplinary committee on the basis of facts has found them guilty of this act, which amounts to gross indiscipline and recommended that they be suspended from the membership of the party immediately," Party General Secretary in-charge of Organisation Janardan Dwivedi said.
He said the Congress President has accepted the recommendation of the disciplinary committee and therefore "Singh and Brar have been suspended from the party with immediate effect".