In a massive jolt to the opposition Congress in Meghalaya, 12 of its 17 MLAs led by former chief minister Mukul Sangma will join Mamata Banerjee's Trinamool Congress on Thursday, said one of the defecting lawmakers H M Shangpliang.

"Twelve MLAs of the Congress out of 17 in Meghalaya have decided to join the TMC. We will formally join the TMC under the leadership of former CM Mukul Sangma," Shangpliang, the MLA from Mawsynram in East Khasi Hills district told PTI late Wednesday night.