In 1957 Kuroń graduated from the Faculty of History at the University of Warsaw. In 1964, together with Karol Modzelewski, he wrote "The Open Letter to the Party". In this letter he criticized a new ruling and bureaucratic class. He suggested replacing the existing system with workers' democracy, including organizing a referendum according to which major decisions concerning a distribution of national income would be made. The immediate aim was to have a consent of all workers to make decisions on economic plans. Kuroń's critique was closely related to the ideas of Marxism and Trotskyism. In 1965, he was sentenced to three years in prison for writing "The Open Letter to the Party". Kuroń defiantly sang "The Internationale" in court. Imprisoned in Wronki Prison, he was released in 1967, and soon arrested again. In 1968 Kuroń was sentenced to three and a half years in prison for organizing student strikes during March Events. In 1975, he helped to organize a protest against the passage of amendments to the Constitution of the People's Republic of Poland. Following a government crackdown on strikes, and the jailing of striking workers, in June 1976, Kuroń co-founded with Antoni Macierewicz KOR, a worker's defense committee and civil organization that helped pave the way for Solidarność (). The Coastal Free Trade Union WZZ, the cradle of Solidarity, was established on April 29, 1978 after Krzysztof Wyszkowski convinced Kuron that workers needed their own voice.