Around five Chief Ministers have sent their recorded message or written speech to Chief Minister Arvind Kejriwal conveying their inability to participate in the conference due to pressing issues.
The conference, a brain-child of Kejriwal, will discuss various aspects of the co-operative federalism and the "strain" it has witnessed during the current regime at the Centre, officials said.
Kejriwal, who has been at loggerheads with the Centre over sharing of power, had extended invitations to chief ministers of all states, including those ruled by BJP and Congress.
West Bengal Chief Minister Mamata Banerjee and Tripura Chief Minister Manik Sarkar have already confirmed their participation.
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Bihar Chief Minister Nitish Kumar, who is busy with preparations for Assembly polls in his state, and Mizoram's Lal Thanhawla have sent their written messages which will be read out at the conference.
Last month, Kejriwal had announced hosting of the conference at a programme where he had felicitated his Bihar counterpart, Kumar.
In July, Kumar had met Kejriwal at Delhi Secretariat and come out in support of full statehood for Delhi and had said JD(U), in coordination with other parties, would raise the issue in the Parliament.