The police have denied permission on various grounds but they cannot be divulged as the matter was sub-judice, Chennai Police Commissioner J K Tripathy told PTI.
Sources said permission was denied on various grounds, including security implications as a large turnout was expected than the venue could accommodate or the organisers had mentioned.
The police decision came late on Friday night hours after the Madras high court, during the hearing of two PILs opposing the conference of the TESO, directed the city police chief to pass a detailed order on the representation (seeking permission) submitted by the organisers and communicate the decision to them immediately.
TESO, a pro-Sri Lankan Tamils outfit floated by Karunanidhi in the late 80s, was recently revived by him and its first meet was scheduled to be held in Chennai on Sunday several leaders besides some Sri Lankan Tamil leaders expected to participate in it.
Both the Central and Tamil Nadu governments had on Friday submitted in the court objections to certain aspects of the conference.
The Centre told the court that it would not allow the organisers, including the DMK, to use the word 'Eelam' in the heading of the international conference, while the state government said it may deny permission for holding the event as the chosen venue was not big enough to accommodate the number of people expected to attend it.
State Advocate General A Navaneethakrishnan said police permission may be denied as the YMCA ground was located near a government hospital, attended by over 3000 out-patients daily.
Besides, according to DMK party organ Murasoli, over one lakh people were expected to attend the meet with about 1,250 vehicles, which may result in traffic diversions in that area, bringing life to a standstill in the city.
Reacting to the police action, Karunanidhi in a statement in Chennai said that all legal steps would be taken for holding the meet as scheduled.
Karunanidhi, who went into a huddle with his senior party colleagues to discuss the development, said the police commissioner's order mentioned they had information that Liberation Tigers of Tamil Eelam activists and other extremist organisations might take part in the meet and described it as "totally untrue".
He said certain efforts were being made to thwart the conference despite the organisers making it clear that it was only aimed at taking up issues relating to the livelihood of Sri Lankan Tamils.
Karunanidhi said they would approach "all judicial forums" and explain their position and seek justice. TESO would take a decision based on the judicial outcome, he added.