The Kerala Congress-Mani, the third largest member in the ruling Congress-led UDF, split on Thursday when four senior leaders decided to quit.
The party has eight legislators but none of them has walked away.
Kerala Congress-Mani is led by former finance minister K.M. Mani, who had to step down last year following a court reference in an alleged corruption case that is known as the bar scam.
Addressing reporters here, senior party leader Antony Raju said they had no option but to quit the party as it had no inner party democracy.
"The party has become the personal fiefdom of Mani and his Lok Sabha member-son Jose K. Mani," said Raju, a former legislator.
He said last month a secret deal had been worked with Bharatiya Janata Party president Amit Shah. "We hear that after the assembly polls (in Kerala), Jose K. Mani will be made a union minister."
The others who have decided to leave the party are Francis George, a former Lok Sabha member, and former legislators K.C. Joseph and P.C. Joseph.
Chief Minister Oommen Chandy said the development won't have any impact on the UDF.
"The UDF is united and in good shape. I will never say anything about those who have left our front," he said in Kozhikode.
Raju added: "We will meet on the 9th of this month to decide the future course of action."
