When the government enacted new food price increases in the summer of 1980, a wave of labor unrest swept the country. Partly moved by local grievances, the workers of the Lenin Shipyard in Gdansk went on strike in mid-August. Led by electrician and veteran strike leader Lech Walesa, the strikers occupied the shipyard and issued far-reaching demands for labor reform and greater civil rights. The workers' top priority was establishment of a trade union independent of communist party control and possessing the legal right to strike. Buoyed by a wave of popular support and formally acknowledged by other striking enterprises as their leader, the Gdansk workers held out until the government capitulated. The victorious strikers hailed the Gdansk Agreement of August 31 as a veritable social contract, authorizing citizens to introduce democratic change to the extent possible within the confines of the communist system.

Solidarity, the free national trade union that arose from the nucleus of the Lenin Shipyard strike was unlike anything in the previous experience of Comecon nations. Although primarily a labor movement led and supported by workers and represented by its charismatic chairman Walesa, Solidarity attracted a diverse membership that quickly swelled to 10 million people, or more than one of every four Poles. Because of its size and massive support, the organization assumed the stature of a national reform lobby. Although it disavowed overtly political ambitions, the movement became a de facto vehicle of opposition to the communists, who were demoralized but still in power. With the encouragement of Pope John Paul II, the church gave Solidarity vital material and moral support that further legitimized it in the eyes of the Polish population.

In the sixteen months following its initial strike, Solidarity waged a difficult campaign to realize the letter and spirit of the Gdansk Agreement. This struggle fostered an openness unprecedented in a communist East European society. Although the PZPR ousted Gierek as first secretary and proclaimed its willingness to cooperate with the fledgling union, the ruling party still sought to frustrate its rival and curtail its autonomy in every possible way. In 1980-81, repeated showdowns between Solidarity and the party-state usually were decided by Solidarity's effective strikes. The movement spread from industrial to agricultural enterprises with the founding of Rural Solidarity, which pressured the regime to recognize private farmers as the economic foundation of the country's agricultural sector.

Meanwhile, the persistence of Solidarity prompted furious objections from Moscow and other Comecon members, putting Poland under constant threat of invasion by its Warsaw Pact allies. This was the first time a ruling communist regime had accepted organizations completely beyond the regime's control. It was also the first time an overwhelming majority of the workers under such a regime were openly loyal to an organization fundamentally opposed to everything for which the party stood. In 1981 an estimated 30 percent of PZPR members also belonged to an independent union.

In late 1981, the tide began to turn against the union movement. In the midst of the virtual economic collapse of the country, many Poles lost the enthusiasm that had given Solidarity its initial impetus. The extremely heterogeneous movement developed internal splits over personality and policy. Walesa's moderate wing emphasized nonpolitical goals, assuming that Moscow would never permit Poland to be governed by a group not endorsed by the Warsaw Pact. Walesa sought cooperation with the PZPR to prod the regime into reforms and avoid open confrontation with the Soviet Union. By contrast, the militant wing of Solidarity sought to destabilize the regime and force drastic change through wildcat strikes and demonstrations.

In 1981 the government adopted a harder line against the union, and General Wojciech Jaruzelski, commander in chief of the Polish armed forces, replaced Stanislaw Kania as party leader in October. Jaruzelski's very profession symbolized a tougher approach to the increasingly turbulent political situation. At the end of 1981, the government broke off all negotiations with Solidarity, and tension between the antagonists rose sharply.