A personal acquaintance of Lev Kamenev and other leading Bolsheviks, Chernyi denounced the nascent Soviet Union at a rally on March 5, 1918, declaring that for anarchists, the socialist state was as much an enemy as its bourgeois predecessor and promising to "paralyze the governmental mechanism". A vociferous advocate of seizing private homes, Chernyi agitated against the state in the pages of Anarkhiia, the anarchist weekly newspaper, proposing increasingly detailed means of decentralized production and "complete absence of internal power structures". In the Spring of 1918, the anarchist groups within the Moscow Federation, formed armed detachments in reaction to the growing repression of all resistance and free expression. These were the Black Guards, precursors to the anarchist Black Army which fought the Bolsheviks in the Russian Civil War. On the night of April 11, the Cheka (Soviet secret police) raided a building occupied by the Moscow Federation, with the official aim of arresting and charging "robber bands" in the anarchist ranks. They were met with armed resistance by the Black Guards and in the ensuing battle, approximately forty anarchists were killed or wounded and about five hundred were imprisoned.
Having helped establish an underground group in 1918, Chernyi joined another group called the Underground Anarchists the following year. The organization, which had been founded by Kazimir Kovalevich and Piotr Sobalev, published two issues of an incendiary broadsheet denouncing the Communist dictatorship as the worst tyranny in human history. On September 25, 1919, together with a number of leftist social revolutionaries, the Underground Anarchists bombed the headquarters of the Moscow Committee of the Communist Party during a plenary meeting. Twelve Communists were killed and fifty-five others were wounded, including eminent Bolshevik theorist and Pravda editor Nikolai Bukharin. Chernyi was detained along with Fanya Baron on a counterfeiting charge. In August 1921, the Moscow Izvestia published an official report announcing that ten "anarchist bandits", among them Chernyi, had been shot without hearing or trial. However, historian of anarchism Paul Avrich contends that Chernyi was executed in September of that year rather than August. Although he was not personally involved in the bombing of the Communist Party headquarters, Chernyi was, because of his association with the Underground Anarchists, a likely candidate for a frameup. The Communists refused to turn over his body to his family for burial, and rumors persisted that he had in fact died of torture.