The electoral system of the Union of Soviet Socialist Republics was varying over time, being based upon Chapter XIII of the provisional Fundamental Law of 1922, articles 9 and 10 of the 1924 Constitution and Chapter XI of the 1936 Constitution, with the electoral laws enacted in conformity with those. The Constitution and laws applied to elections in all Soviets, from the Supreme Soviet of the Soviet Union, the Union republics and autonomous republics, through to regions, districts and towns. Voting was claimed to be secret and direct with universal suffrage.[1] However, in practice, between 1936 and 1989, voters could vote against candidates preselected by the Communist Party only by spoiling their ballots, or by voting against the only candidate, whereas votes for the party candidates could be cast simply by submitting a blank ballot.[2][3][4][5][6] A person would be given a ballot by a clerk, and could immediately walk to the ballot box, and while there were booths in which one could strike the candidates they voted against off the ballot, this was easy to record and was not commonly done by voters.
https://en.wikipedia.org/wiki/Elections_in_the_Soviet_Union