Later, CPIU(ML) broke away from MCPI. CPIU(ML) was mainly based in Bihar and West Bengal.
In August 2003 discussions took place between Kanu Sanyal and Arvind Sinha from CPI and Subodh Mitra and S.D. Bose about a possible merger between CPIU(ML) and CPI(ML). The conference of CPIU(ML) in Samastipur November 18, 2003 confirmed the merger plans, and CPIU(ML) joined the CPI(ML) of Sanyal.