In 1997, due to difference in political views with the then West Bengal Pradesh Congress Committee president Somendra Nath Mitra, Banerjee left the Congress Party in West Bengal and became one of the founding members of the All India Trinamool Congress, along with Mukul Roy. It quickly became the primary opposition party to the long-standing Communist government in the state. On 11 December 1998, she controversially held a Samajwadi Party MP, Daroga Prasad Saroj, by the collar and dragged him out of the well of the Lok Sabha to prevent him from protesting against the Women's Reservation Bill.