MDMK leader Vaiko was arrested near Theni, 500 km west of Chennai, on Wednesday when he was going to take part in a protest against the Kerala government for its stand on the Mullaperiyar dam issue.
Vaiko was arrested along with two others including Tamilar Desia Iyakkam leader Pala
Nedumaran for defying prohibitory orders.
Prohibitory orders are in force due to the tense situation in the wake of the
row between Tamil Nadu and Kerala on the 116-year-old dam. The police said they requested Vaiko not to organise meetings and also informed him about the prohibitory orders.
The Tamil Nadu government, which runs the project, wants to raise the height of the dam. But Kerala is opposing it.