The former speaker, pitted against the NDA's Ram Nath Kovind in the presidential race, stressed that she was fighting for the freedom of speech and expression, and for a free media.
Condemning the "prevailing atmosphere of fear," she said, "Earlier, also, there were religious beliefs and practices, but we never witnessed such an atmosphere of fear."
She said there was fear about what one should eat and say.
"This has to stop," she said, addressing Trinamool Congress MLAs in the West Bengal state assembly.
Ms Kumar separately met MLAs of the Trinamool Congress, Left Front and Congress in the assembly and thanked them for pledging their support to her in the July 17 election.
"It is a fight of two ideologies. I am fighting an ideological battle. I am fighting for the ideology of equality, democratic values freedom of expression and speech," she said.
Ms Kumar appealed to the lawmakers to listen to their "voice of conscience", she told the media later.
She said she was "not alone" in the fight and that she had the support of a number of parties and also a large number of people.
"This is for the first time that so many opposition parties have come together, keeping aside their differences, under the leadership of Congress president Sonia Gandhi for the sake of this country," Ms Kumar said.