Led by DMK working president M K Stalin, the opposition parties met Mr Rao at the Raj Bhavan in Chennai and presented a memorandum highlighting their demands.
"The trust vote was won (by the Palaniswami government) only due to horse-trading. So, that voting should be cancelled and this government should be dismissed immediately," Mr Stalin, also the leader of opposition in the state assembly, later told reporters.
These demands have been raised with the governor and he has "assured" us to look into the legal aspects of the matter, Mr Stalin said.
The opposition move comes amid its failed bid to raise in the state assembly the issue of a TV 'sting' operation where O Panneerselvam camp MLA SS Saravanan is purportedly shown making claims of horse-trading of his party legislators ahead of the crucial February 18 trust vote that was won by incumbent Chief Minister E Palaniswami.
The opposition has been denied permission by Speaker P Dhanapal to raise the matter for three consecutive days. The DMK members including Stalin were evicted en masse on Wednesday while the party staged a walkout on the next two days on being denied permission.
In a memorandum submitted to the governor today, Stalin recalled the chain of events preceding the trust vote, such as the revolt of former Chief Minister O Panneerselvam against party chief V K Sasikala and her conviction in a disproportionate assets case.
He said AIADMK MLAs were later taken to a seaside resort at Koovathur near here and "detained illegally" prior to the trust vote and later brought to the assembly for voting.
DMK, as a "responsible opposition party" had demanded then that the speaker should either order for a secret ballot or adjourn proceedings for a week to make sure that the MLAs cast their "votes in a cordial atmosphere with free will and consent," he said.
But none of the demands were heeded to, he said.
"The very basic features of the floor test in the House stand defeated mercilessly and recklessly. The speaker failed to conduct a real lawful test in the House and in the pandemonium which followed, the speaker declared that the motion of confidence moved by the newly appointed chief minister has been passed and he has won the vote of confidence," he said.
The DMK had then itself urged the governor to nullify the floor test, he said, recalling it had also moved the Madras High Court challenging the validity of the trust vote.
On the TV 'sting' operation about alleged horse-trading of AIADMK MLAs ahead of the trust vote, Stalin said Madurai South MLA SS Saravanan belonging to AIAADMK Puratchi Thalaivi Amma had made claims in this regard.
"It is me in the video, but the voice is not mine," Mr Saravanan had said.
Mr Stalin further said in the memorandum that "we state, therefore, that the video recordings of the sting operation constitutes material evidence which has a significant bearing on the validity of the proceedings of the vote of confidence."
The "sting operation" was "important evidence" regarding the circumstances in which the confidence vote was held, he said.
Despite their repeated pleas in the first three days of the ongoing assembly session, the speaker had refused to take up the matter for discussion, he said.
The video-footage of the 'sting' operation "reveal that the vote of confidence was vitiated by inducements and bribery of the AIADMK MLAs," he alleged.
Allegations of AIADMK MLAs having taken illegal gratification to cast votes then "is now corroborated by the material that has come to light through independent media sources," he said.
"These actions of inducement, bribery and illegal gratification, if proved true, throw our entire democratic system in peril and also require investigation for offences under Prevention of Corruption Act, Income Tax Act and Prevention of Money Laundering Act," Mr Stalin said.
The governor should, therefore, "order for a fresh vote of confidence" and direct an impartial investigation by the CBI into the offences of Prevention of Corruption Act," he said.
The governor should also direct an investigation by the Directorate of Revenue Intelligence or ED "to unearth the money trail and to investigate the offences under the Prevention of Money Laundering Act," Mr Stalin added.
Mr Stalin, accompanied by Congress Legislature Party Leader K R Ramasamy and Indian Union Muslim League MLA KAM Mohammed Abubakker, said the opposition parties will discuss the future course of action if the governor did not act on their demands.