 With the ongoing Revolution of 1905 the party was reformed based on already existing Revolutionary Ukrainian Party (RUP) based from Kharkiv in December 1905 at the 2nd Party Congress of RUP.The party adopted the Erfurt Program of Social Democratic Party of Germany.In December 1905, the Ukrainian Social-Democratic Labour Party (USLDP) decided to join the Russian Social Democratic Labour Party, provided it was recognised as "the sole representative of the Ukrainian proletariat", within the RSDLP.