He became a member of the
Socialist Workers' Party of Yugoslavia (communists) in 1919 in Osijek, distinguished himself and was a member of the Local Committee of the CPY for Zagreb. In 1920, the Yugoslav government banned Obzan from the Communist Party. However, the unresolved Croatian issue was far more dangerous for the government than the communist activity. At the beginning of 1923, the communists illegally founded the Independent Workers' Party of Yugoslavia. In the same year, Hebrang settled in Zagreb. He was first arrested for street demonstrations in March 1924, after which he spent several days in prison. In the 1925 elections, the Independent Workers' Party won only 1.1% of the vote and was left without a seat in the National Assembly. The following year, Hebrang joined the Board of Directors of a branch of the Union of Private Employees as treasurer, and before their congress in October 1927 he was expelled from the union and administration. In 1928, Pantovčak was presided over by VIII. conference of the Zagreb Communists where, together with Tito, he opposed factional struggles within the Party. The victory of their anti-factional current, with the support of Antun Mavrak, secretary of the CPY Provincial Committee for Croatia and Slavonia, enabled the consolidation of party ranks. Hebrang was appointed an envoy of the Zagreb Local Committee at the April session of the
Comintern in
Moscow, but was arrested on April 13, 1928, while crossing the border. He was detained for three months for "wandering and communism," but was soon released for lack of evidence. He was expelled to Bačevac, but returned illegally to Zagreb, where, after the murder of
Pavle Radić and Đuro Basaričko, the wounding of
Ivan Pernar and Ivan Granđa, and the fatal wounding of
Stjepan Radić in the National Assembly on June 20, 1928, the work of the Party intensified. Following the assassinations, the ensuing protests intensified police persecution of opponents of the regime, especially HSS members and communists.
Imprisonment (1928–1941) In Zagreb, meanwhile, the management of the Workers' Cultural Society, of which Hebrang was a member, was arrested and served a month in prison. At the same time, he was expelled to Bačevac for five years, but as soon as the circumstances allowed, he returned illegally to Zagreb. Hebrang was arrested again on September 7, 1928, together with Mihail Vraneš, in Zagreb, in front of the house in Gundulićeva Street, where the secret Party archives were located. Because he was arrested with compromising letters and documents, he was taken to remand prison. At that time, communism, under the State Protection Act, was characterized as a coup d'état, which made it impossible to punish Hebrang more leniently. At the trial in Belgrade, he did not admit his affiliation with the Communist Party, but declared himself a communist by conviction. As his communist activity was indisputably proven, the State Court for the Protection of the State sentenced him, on November 13, 1928, to 12 years in prison. He was sent to serve his sentence in Lepoglava, but at the end of 1933, together with other political prisoners, communists, he was transferred to Srijemska Mitrovica, because after the strike in Lepoglava the penitentiary administration decided to gather political prisoners in one place. In March 1941, shortly after his release from prison, he became a member of the Central Committee of the
Communist Party of Croatia. ==World War II==