The core of the party was formed in a few days, with several clandestine youth organizations joining the National United Party. The new party produced its bylaws and program of activities. On April 24, 1967, the declaration of the NUP was presented in an event near the nearly finished genocide monument on the hill of Tsitsernakaberd. The first members of the party made their sacred pledge to be faithful to the ideas of the party. The NUP Council became the leading body of the party. All members should closely follow the program of the party, entitled “For the Nation and the Homeland.” Any person aged sixteen, who accepted the program, the bylaws, and the sacred pledge, could become a party member. Its structure was composed of ten-member groups, which did not maintain contact and did not know each other. Each group had a leader, who knew the other group leaders, as well as their main leader (captain). The goal of this structure was to maintain the secrecy in the activities of the group.
The NUP produced the first issue of its clandestine periodical Paros (Phare) in October 1967. In an article published with the pseudonym Vram, Haykaz Khachatryan wrote: “Armenian nation, your holy duty is to be faithful to the work of your ancestors, maintain the national identity, struggle for the independence of Armenia. April 24 must be commemorated every year. It must be a day of wrathful protest against the crimes of the past and the present.”
The publication made waves not only in Armenia and the Soviet Union, but also abroad. It disclosed the existence of the party to all quarters where anti-Soviet movements were being formed. Paros was indeed forbidden and labeled as anti-Soviet. Its writers and readers were persecuted. New members joined the National United Party, but this became the cause for its fall, as traitors entered the field. Khachatryan was arrested in June 1968, together with Zatikyan and Harutyunyan, and condemned to five years of prison by the Supreme Court of Armenia on charges of anti-Soviet agitation and participation in an anti-Soviet organization. Khachatryan would be released in 1973 and imprisoned again from 1978-1980; Zatikiyan would be released and then shot by the Soviet regime in 1979; Harutyunyan would later migrate to California and head a movement of support to Armenian dissidents and political prisoners.
Hayrikyan was elected president of the party in 1973. He was arrested again in 1974 and spent the next thirteen years in prison, continuing clandestinely to lead the organization. On his return to Armenia in August 1987, he founded a successor party to the NUP, the National Self-Determination Union, which was quite active in the first years of the Gharabagh movement and still continues its existence as a political party. Other members of the National United Party would become leaders of the Gharabagh movement, such as Movses Gorgisian (1961-1990), or the Republican Party of Armenia, like its founder Ashot Navasardian (1950-1997), or future prime minister Andranik Margaryan (1951-2007).