They took out a procession from neighbouring Pillaithottam and were held on their way to Raj Nivas, police said.
Among those held included national council member of CPI N Kalainathan, AITUC secretary V S Abishegam, farmers wing leader N Geethanathan and CPI's town secretary K Murugan.
They raised slogans condemning the "negative stand of Lt Governor Kiran Bedi" in routine administration.
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