"It is still not late. Don't just stop with passing a resolution in the Assembly. Convene the Cabinet and adopt a resolution (seeking their clemency)," he told the Jayalalithaa government.
Karunanidhi said his government had adopted a similar approach in the case of two death row convicts and former Naxalites, Thyagu and Kaliyaperumal.
Addressing a function to commemorate the birth anniversaries of Dravidian icons E V R Periyar and C N Annadurai besides his party's founding, Karunanidhi said the convicts -- Murugan, Santhan and Perarivalan -- had spent nearly 20 years in prison for the former prime minister's killing.
Tamil Nadu Assembly had recently passed a resolution urging President Pratibha Patil to reconsider the mercy plea of the trio, which she had rejected earlier.
"Once such a resolution is forwarded to the governor who in turn sends it to the Centre, it should also come forward to save them. This is our plea and request," he said.
On a petition from the three convicts, the Madras High Court earlier this month stayed their execution for eight weeks.