The Communist Party of the Soviet Union (CPSU), at some points known as the Russian Communist Party (Bolsheviks) and the All-Union Communist Party (Bolsheviks), and sometimes referred to as the Bolshevik Party and Soviet Communist Party, was the founding and ruling political party of the Soviet Union. The CPSU was the sole governing party of the Soviet Union until 1990 when the Congress of People's Deputies modified Article 6 of the 1977 Soviet Constitution, which had previously granted the CPSU a monopoly over the political system. The party's main ideology was Marxism–Leninism. The party was outlawed under Russian president Boris Yeltsin's decree on 6 November 1991, citing the 1991 Soviet coup attempt as a reason.