They were charged with IPC 309 (attempt to commit suicide) read with (punishment of abetment), Inspector of Police P M Manoj told PTI.
A case was also registered against Anjana, who allegedly tried to commit suicide, he said.
Anjana had made a vain suicide attempt soon after being released on bail after the arrest. She is undergoing treatment at a nearby hospital and her condition is stable now.
The sisters, Akhila and Anjana, had been summoned to the police station on June 17 and a case was registered against them for allegedly attacking a CPI(M) worker and trespassing into the party office.
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The two were released the next day after the National Commission for Scheduled Caste intervened.
According to CPI(M)'s complaint, the women had barged into the party office here and attacked one of their activists recently.
National Commission for Scheduled Caste Commission representative P Girija visited the siblings and recorded their statements. She also collected details from investigators probing the case.
The state SC/SC Commission Chairman Justice P N Vijayakumar and other members also called on the women and family members.