Trinamool Congress MLA Shilbhadra Dutta tendered his resignation from the party on Friday morning in what has been the third such exit for the ruling party in West Bengal.
The resignation comes just a day after TMC MLAs Jitendra Tiwari and Suvendu Adhikari had also decided to quit the party.
The rebels are expected to join the rival Bharatiya Janata Party (BJP).
Dutta tendered his resignation to TMC supremo and West Bengal Chief Minister Mamata Banerjee via email on Friday morning.
"I think I am unfit for the party in the present scenario. But, I will not resign as an MLA," the MLA told reporters. "Why should I resign as an MLA? I have won by people's votes. If I resign, where will they go?"
Dutta, who represents the Barrackpore seat, has been vocal about his opposition to the TMC's ties with election strategist Prashant Kishor over the last few months.
A two-term MLA, Dutta has also spoken against a section of the party's leadership.
Notably, Dutta was once loyal to former TMC leader Mukul Roy, who is now associated with the BJP.
On Thursday, Suvendu Adhikari had resigned from the party nearly a month after resigning as the Minister of Transport and Irrigation in West Bengal.
It is speculated that Adhikari's resignation will trigger an exodus from the TMC to the BJP.
Adhikari—who had been central to Banerjee's rise in Bengal politics—is said to have control over local leaders in at least 50 Assembly seats.
After Adhikari's resignation, Tiwari also quit the party on Thursday.
Meanwhile, TMC MP Sunil Mandal and Bengal Forest Minister Rajib Banerjee have also criticized the party.
Adhikari will likely join the BJP on Saturday when Union Home Minister and former BJP President Amit Shah visits the state ahead of Assembly elections next year.
The BJP is eyeing 200 of the state's 294 Assembly seats.
Love Politics news?
Subscribe to stay updated.