The Solidarity movement in Poland staged a warning strike, the largest in the history of the Eastern Bloc, in which at least 12 million Poles walked off their jobs for four hours.

Solidarity, full name Independent Self-Governing Trade Union "Solidarity", is a Polish trade union founded in August 1980 at the Lenin Shipyard in Gdańsk, Poland. Subsequently, it was the first independent trade union in a Warsaw Pact country to be recognised by the state.

The 1981 warning strike in Poland was a four-hour national warning strike that took place during and in response to the Bydgoszcz events. There, in the early spring of 1981 in the Polish People's Republic, several members of the Solidarity movement, including Jan Rulewski, Mariusz Łabentowicz, and Roman Bartoszcze, were beaten by the security forces, including Milicja Obywatelska and ZOMO. The Bydgoszcz events soon became widely known across Poland, and on 24 March 1981, Solidarity called for a nationwide strike in protest against the violence. The strike was planned for Tuesday, 31 March 1981. On 25th March, Lech Wałęsa met Deputy Prime Minister Mieczysław Rakowski of the Polish United Workers' Party, but they were unable to come to an agreement. Two days later, on 27th March, the warning strike took place. It was the most highly participated strike in the history of both Poland and the Warsaw Pact. According to several sources, between 12 and 14 million Poles took part, roughly 85-90% of Poland's working-age population at the time.

The Eastern Bloc, also known as the Communist Bloc (Combloc), the Socialist Bloc, the Workers Bloc, and the Soviet Bloc, was an unofficial coalition of communist states of Central and Eastern Europe, Asia, Africa, and Latin America that were aligned with the Soviet Union and existed during the Cold War (1947–1991). These states followed the ideology of Marxism–Leninism, in opposition to the capitalist Western Bloc. The Eastern Bloc was often called the "Second World", whereas the term "First World" referred to the Western Bloc and "Third World" referred to the non-aligned countries that were mainly in Africa, Asia, and Latin America but notably also included former pre-1948 Soviet ally Yugoslavia, which was located in Europe.