The decision follows a communication from TMC national general secretary Abhishek Banerjee that asked the speaker to reject the merger request, since the TMC was “a single, indivisible political party” and there was no option of a split under the Tenth Schedule of the Constitution.

Birla’s office had issued a letter to Abhishek Banerjee, the TMC floor leader in the Lok Sabha, for a meeting on Monday, but it could not take place because Abhishek was being grilled by investigative agencies at the time.

“Speaker Om Birla will take a call on the issue of the merger of 20 TMC MPs with NCPI only after hearing both sides. The Speaker’s office has also emailed TMC, led by Mamata Banerjee,” said a senior official aware of the details.

In a meeting with Birla on Sunday evening, 19 TMC lawmakers handed over a letter expressing their wish to join the NCPI. Rachana Banerjee, a first-time MP currently in Malaysia, gave her consent in the letter, bringing the group to 20 lawmakers.

“This is a part of the standard protocol before a decision on a split or merger is taken. It is highly unlikely that the merger would be rejected due to TMC’s objections,” said a senior Opposition leader.

On Birla calling Mamata Banerjee-led TMC MPs for a meeting, TMC MP Saugata Roy said it was a good thing. “It is the Speaker’s duty to be unbiased. Before the dissatisfied MPs submitted a letter, the Trinamool Congress had already submitted one. I have heard that the Speaker has also written to the Trinamool Congress as well to meet their MPs. I don’t know if this letter was received by Trinamool Congress”

“There are many contradictions among those who have left. Some of them want to create another group, some want to join the BJP, and they have joined NCPI. We can already see different opinions within the same group,” Ray said.

The merger of the rebel group with NCPI would increase the NDA’s strength from 294 to 314 in the Lok Sabha — still short of 46 seats to secure the magical two-thirds majority in the Lower House. In the Upper House, the ruling dispensation can reach 155 seats, just 8 seats short of the two-thirds majority.

A BJP MP, who was involved in the process, said the NCPI was an unrecognised party which fought polls in West Bengal, Tripura and Meghalaya.

“The decision to merge with NCPI was taken to retain the rebels’ connection with West Bengal, but also give North East a better representation in the Lok Sabha,” the MP said.

The crisis in the TMC was triggered after the party lost the assembly polls last month to the Bharatiya Janata Party (BJP), which formed its first-ever government in the eastern state. In Bengal, 59 MLAs formed a breakaway faction with Ritabrata Banerjee as the Leader of the Opposition in the assembly, and Dastidar voiced her dissent after she was dropped from the chief whip’s post.