Ghetto benches (known in Polish as getto ławkowe) was a form of official segregation in the seating of university students, introduced in 1935 at the Lwow Polytechnic. Rectors at other higher education institutions in the Second Polish Republic had adopted this form of segregation when the practice became conditionally legalized by 1937. Under the ghetto ławkowe system, Jewish university students were required under threat of expulsion to sit in a left-hand side section of the lecture halls reserved exclusively for them. This official policy of enforced segregation was often accompanied by acts of violence directed against Jewish students by members of the ONR (outlawed after three months in 1934). The seating in benches marked a peak of antisemitism in Poland between the world wars according to Jerzy Jan Lerski. It antagonized not only Jews, but also many Poles. Jewish students protested these policies, along with some Poles who supported them by standing instead of sitting. The segregation continued until the invasion of Poland in World War II. Poland's occupation by Nazi Germany suppressed the entire Polish educational system. In the eastern half of Poland annexed by the Soviet Union, similar discriminatory policies were lifted and replaced with other repressive actions against Jews. The percentage of Poland's Jewish population increased greatly during the Russian Civil War. Following Poland's return to independence, several hundred thousand Jews joined the already numerous Polish Jewish minority living predominantly in the cities. The new arrivals were the least assimilated of all European Jewish communities of that period. Jews formed the second largest minority after Ukrainians, of about 10 percent of the total population of the Polish Second Republic. Jewish representation in the institutions of higher learning began to increase already during World War I. By the early 1920s, Jewish students constituted over one-third of all students attending Polish universities.