During this period, Grossman learned Yiddish and became involved in the Jewish workers' movement in Kraków. Grossman was the founding secretary and theoretician of the Jewish Social Democratic Party of Galicia (JSDP) in 1905. The JSDP broke with the PPSD over the latter's belief that the Jewish workers should assimilate to Polish culture. It took a position close to the Bund, and was critical of the labour Zionism of the Poale Zion as well to assimilationist forms of socialism. The JSDP sought to affiliate to the Social Democratic Workers' Party of Austria (the General Party), but this was refused. However, the JSDP was active alongside the General Party, for example for universal suffrage.