Mr Bardhan moved to Delhi politics in the 1990s and became the Deputy General Secretary of the CPI.
The condition of CPI veteran AB Bardhan, who was admitted to a hospital here on Monday after he suffered a paralytic stroke, is "very critical", party national secretary D Raja said today.
"He is very critical. Doctors are making efforts to see his health gets better," Rajya Sabha member D Raja said.
Mr Bardhan, 92, is in the ICU at the GB Pant hospital.
He could open eyes and showed a little movement in left leg, another CPI leader Atul Anjan had said yesterday.
"But there was not much improvement observed later in the day," he said.
Ardhendu Bhushan Bardhan has been a leading figure of the trade union movement and Left politics in Maharashtra. He had won as an Independent candidate in the Maharashtra Assembly in 1957.
He later rose to become the General Secretary and then the President of the All India Trade Union Congress, the oldest trade union in India.
Mr Bardhan moved to Delhi politics in the 1990s and became the Deputy General Secretary of the CPI. He succeeded Indrajit Gupta as the General Secretary of the party in 1996.