Speaking to reporters here, he said Murugan, Santhan and Perarivalan had assassinated the Prime Minister and a leader of great stature and if they are released it will only set a bad precedent.
"The decision (of Tamil Nadu government) is shocking, unacceptable and embarrassing and hence they should reconsider it," he said and pointed out that life term meant they should be incarcerated till the end of their lives.
But now the AIADMK government in Tamil Nadu had taken an "arbitrary" decision to release them, Narayanasamy said.
He said the state government had no constitutional authority to take such a decision as the case was probed by CBI and the culprits were punished under provisions of TADA.
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"This U turn gives rise to suspicion that AIADMK is now seeking political mileage and eyeing the Lok Sabha polls," he said.
"Merely because there was delay on the part of the Centre to take a decision on mercy petitions submitted by the convicts does not mean that the capital punishment can be reduced to life term", he said.
On February 19, the Tamil Nadu government decided to release all seven convicts serving life term in the Rajiv Gandhi assassination case, a day after Supreme Court commuted the death penalty of Murugan, Santhan and Perarivalan.