The 1981 strike at the Piast Coal Mine in Bieruń was the longest underground protest in the postwar history of Polish mining, and the longest strike of the martial law in Poland. It began on December 14, 1981, one day after introduction of the martial law, and ended on December 28, when approximately 1,000 protesting miners emerged from the mine. They spent two weeks underground, including Christmas, and ended the protest after the government guaranteed their safety.