From the perspective of human rights, the Soviet Union was arguably the black sheep of the Allies in World War II.

Until his death in 1953, Joseph Stalin ruled the country as a de facto dictator. His communist government didn't allow political dissent, and Stalin imprisoned people suspected of harboring subversive ideas (source). Censorship laws in the Soviet Union made sure that information didn't circulate if it contradicted the ideology of the Communist Party. Religion was outlawed because the communist philosophy considered it a tool to oppress the working class.

Historians debate just how many people lost their lives as a direct result of Stalin's oppressive policies. Some think he was actually more lethal than Hitler.

So it's not super surprising that the Soviets weren't all in favor of the Universal Declaration of Human Rights.

Of course, the Soviet Union didn't raise its hand and say, "We disagree with this idea because we want to keep oppressing people." From the communist perspective, individual rights enshrined in the declaration, like freedom of expression, were a threat to the one-party system. Leaders of the Soviet Union argued that human rights could only be exercised through the government. They were cool with the inclusion of "positive rights" in the declaration, like the right to social security. In contrast, the democratic traditions of Western countries focused on "negative rights"—things that the state was not allowed to do (source).

The Soviets, and several other communist countries effectively under Soviet rule, didn't support the adoption of the UDHR in 1948. For basically the rest of the 20th century, the United States and the Soviet Union were at each other's throats over these issues. The Cold War pitted the countries' two ideologies against each other, and the U.N. was often the forum for their showdowns.