What country denied membership in NATO in 1954?

In 1954, the Soviet Union proposed a collective security arrangement that included its satellite states, leading to the denial of NATO membership to those countries. However, the most notable denial of NATO membership occurred when the Soviet Union itself sought to join NATO but was rejected. The Western powers were unwilling to include the USSR in the alliance, viewing it as a threat to their security. This rejection highlighted the growing divide between the Eastern and Western blocs during the Cold War.