"The Politbureau of the CPI(M) has unanimouisly decided to expel Somnath Chatterjee from the membership of the party with immediate effect," a party statement said after a meeting of its Politbureau.
"This action has been taken under Article 19 (13) of the party constitution for seriously compromising the party position," it said.
Among those who attended the Politbureau meeting were General Secretary Prakash Karat, Sitaram Yechury, M K Pandhe, S R Pillai and Brinda Karat.