The Łódź insurrection, also known as the June Days, was an uprising by Polish workers in Łódź against the Russian Empire between 21–25 June 1905. This event was one of the largest disturbances in the Russian-controlled Congress Poland during the Russian Revolution of 1905. Poland was a major center of revolutionary fighting in the Russian Empire in 1905–1907, and the Łódź insurrection was a key incident in those events.