Two senior leaders and 600 members of the National Students' Union of India (NSUI), led by its state chief Bansharailang Pyngrope, have now parted ways.
State Congress leader and MLA, Ampareen Lyngdoh filed the disqualification petition against the 10 legislators. A similar petition will be filed against the remaining two.
Sangma said that the entire Northeast wants a "true alternative" to the Congress that can sincerely take on the BJP and promote the interests of the people of the region.
Sangma's expected elevation was formalised during the first legislative party meeting of the AITC held at the residence of the former Congress leader in Shillong.
'Party leadership looking into this conspiracy': Kharge on 12 Meghalaya Congress MLAs joining Trinamool
The party went into a huddle after the exodus of its MLAs in Meghalaya amid problems within its local unit.
Metbah Lyngdoh said he has also received another letter from TMC national general secretary Abhishek Banerjee who recognised the 12 legislators as members of his party.
Senior Congress leader Ampareen Lyngdoh said the AIIC is mulling legal action into the development but nothing has been finalised.
He said people believed the Congress was failing to respond to its call of duty as the main opposition party in the country.
The switchover will surely deal a body blow to the Congress which is batting infighting. The state will go to elections in February 2023.
Sources said that with an eye on the Meghalaya polls in 2023, team members of poll strategist Prashant Kishor are in Shillong to weigh in TMC's options in the state.
The Congress in Meghalaya was virtually divided into two factions after Pala, who is the Shillong MP, was appointed the state chief by the AICC.
Former CM Mukul Sangma and Meghalaya PCC chief Vincent H Pala have not been getting along well ever since the latter was appointed the new Meghalaya unit chief.
The Congress announced the first list of candidates for the Meghalaya Assembly polls which also includes the name of Chief Minister Mukul Sangma.
The committee met at the residence of Mukul Sangma during the day to discuss the names of candidates for the ensuing assembly poll.
Meghalaya Chief Minister Mukul Sangma on Friday accused the BJP-led NDA central government at the Centre of trying to legalise immigrants by proposing to amend the Citizenship Act.