Chief Minister K Palaniswami said the case had been registered by the police and investigation was on.
He was responding to Leader of Opposition MK Stalin (DMK) and Congress members who raised the issue of EC asking the state chief electoral officer to lodge a police case on the alleged bribing of voters in RK Nagar constituency in north Chennai.
"A probe is on," he said citing the EC's directive to the CEO which was referred in an RTI reply to a Chennai-based advocate.
However, DMK members were on their feet after Mr Palaniswami's reply saying they were not satisfied with his response.
Later, they staged a walkout. The DMK's allies the Congress and the lone IUML member followed suit.
Earlier, soon after the Question Hour ended, Stalin sought adjournment of the House to debate the EC's directive.
Speaker P Dhanapal allowed the DMK leader to raise the issue but asked him not to get into the details of it, saying there was not much time to obtain sufficient inputs from the government.
Later, some remarks made by Stalin in connection with the issue were expunged by the Speaker.
The issue of EC's directive came to fore after a copy of its response to a plea under the Right to Information Act by the city-based lawyer MP Vairakkannan was circulated to media yesterday.
The EC said it had directed the state CEO on April 18 to ask the RK Nagar returning officer to file a complaint with police for bribing the voters.