In July 1928, Kosior was appointed General Secretary of the Ukrainian SSR Communist Party. His return coincided with Stalin's decision to drive the peasants onto collective farms, a policy Kosior supported. Speaking to the Central Committee of the Communist Party of the Soviet Union, in November 1929, he argued that collectivisation was the only way to make progress in agriculture. In February 1930, he declared that Ukraine would be "completely collectivised in the course of the spring sowing campaign."[2]
In July 1930, he was elevated to the Politburo of the Communist Party of the Soviet Union. After the harvest in 1931, Kosior knew that collectivisation was causing a catastrophic fall in agricultural output in Ukraine - visiting Moscow in August, he warned Stalin's deputy, Lazar Kaganovich, that there would be a shortfall of 170 million poods (nearly three million tons) of grain, but Kaganovich blamed the problem on mass theft by Ukrainian peasants and forced Kosior to follow this opinion.[3][4]
Addressing a plenum of the Central Committee of the Communist Party of the Soviet Union (of which he had been a member since 1926) he blamed the failure on middle ranking officials and party members who listened to the complaints of peasants that the quotas were too high. "Not only did they not fight; not only did they fail to organise the collective farm masses in the struggle for bread against the class enemy, they often followed along with this peasant mood", he said.[5]
On Stalin's orders, Kosior pushed through a decree “On grain procurements” on 15 January 1932, which increased the power of the central government in Kharkiv to direct the confiscation of grain in the regions. The fact that he imposed this measure, "in spite of starvation in Ukrainian villages", was the first several examples cited by the Kyiv Court of Appeal in its 2010 resolution that judged Kosior to have been complicit in genocide.[6] The court also recorded that on 1 February, he and Vlas Chubar co-signed a decree “On Seed”, directing local committees to deny any seed aid to Ukraine’s collective farms; on 17 March he signed a decree “On seed reserves”, which led to increased repression of peasants who were resisting the confiscation of grain; and on 29 March, he pushed through a decree “On Polissia", under which 5,000 peasant families were deported from the Polissia region of Ukraine.[6]
In April 1932, after touring the countryside, Kosior wrote to Stalin to say that there had been trouble from hungry peasants refusing to sow grain, and delicately requested that food be sent to Ukraine, which prompted an angry rejection, and seemingly made Stalin suspect that Kosior was not ruthless enough.[7] "The worst aspect of this situation is Kosior's silence," he told Kaganovich, when other leading Ukrainian communists pleaded for help. When Kosior submitted a formal request for relief to the Politburo in Moscow, in June it was turned down flat, and Kaganovich warned him his "mistakes" would be held as an example to other regional party leaders of how not to do their job. This was because Kosior's attempt to find an accommodation between Moscow's demands and the crisis in the countryside had turned Stalin against him. He told Kaganovich that Kosior was "manoeuvring" and engaging in "rotten diplomacy" and being "criminally frivolous." He considered sacking Kosior and sending Kaganovich in his place.[8] However, Kosior and his deputy, Pavel Postyshev, met Stalin, who agreed to reduce Ukraine's grain quota. That seemed to settle their differences.
In November, Kosior delivered a speech blaming the trouble in the countryside on Ukrainian nationalists.[9] In 1935 he was awarded the Order of Lenin "for remarkable success in the field of agriculture".[10]