[3] [7] The detractors and critics of the Shillong Accord maintained that the Clause 3 that stated "reasonable time for the underground representatives to formulate other issues for discussion for the final settlement," still remained unimplemented -- as most of the Naga people and the Naga National Council leaders abroad didn't agree to endorse the agreement.
They even criticized saying that the agreement was signed by "representatives of the Naga underground," rather than the organizations like NNC or the Federal Government of Nagaland.
[4][5][8] However, many Nagas, who were not reconciled being part of Indian union of states, condemned the agreement that ultimately created factionalism among the rebels.
Some critics also point out that Phizo, then-NNC president and who was in exile from 1956 in London, neither endorsed nor renounced the agreement; though, his younger brother Kevi Yalley represented underground organizations and signed Shillong Accord.
[4][5][6] Both Isak and Muivah after five years of signing the accord, decided to restore the damaged image of the NNC for having accepted the Indian constitution, openly rejected the agreement terming it as a "betrayal" by the NNC and censured it as a complete "sell-out" of the Naga rights, including derogatory remarks against Phizo, and swore to fight for unquestionable sovereignty; thus, the trio Muivah, Isaac and S. Khaplang created National Socialist Council of Nagaland(NSCN) breaking-up[abandoning] from their old organization NNC on 2 February 1980.