"The government can negotiate with whomever it wants. But any attempt to impose Amani on us will fail," he said, referring to the UN-sponsored programme launched in January in an attempt to end the simmering conflict in the east of the country.
It was intended to bring all the combatants in the North and South Kivu regions together for talks.
Lambert Mende, the government communications minister, said that about 20 other groups had been invited and criticised the CNDP for threatening to pull out its delegation.
"It's their problem if they don't want peace. They'll be held accountable for their acts," he said.
Laurent Nkunda, the renegade general who leads the CNDP, and Joesph Kabila, DR Congo's president were not expected to attend the meeting in Nairobi, the Kenyan capital.
Nkunda declared a unilateral ceasefire in late October when his fighters were on the verge of overrunning the provincial capital, Goma.
Clashes have continued between the CNDP and local Mai Mai militia and Rwandan Hutu rebels despite the ceasefire.
Representatives of the pro-government Mai-Mai have threatened to withdraw from the peace process if the CNDP are granted separate talks with the government.
"To proceed in this way is to incite us to quit the Amani programme, the government should not forget this," Mai Mai leaders said in a statement given to the AFP news agency.
"We are not a negligible group, we have arms."
Two years of sporadic fighting between Nkunda's fighters and government soldiers supported by local militiamen have forced nearly one million people to flee their homes in North Kivu.