State officials, local leaders and residents gathered at a memorial to the victims of the December 1970 workers' massacre in the Baltic port of Gdynia on Sunday morning, Poland's PAP news agency reported.
Participants sang the national anthem, lit candles and held a roll call of the fallen workers.
President Andrzej Duda issued a message to mark the occasion, which was read out at the ceremony.
The president paid tribute to the "courage, integrity and determination" of the "heroes of December 1970," who were "killed by the communist regime" for "standing up for the rights and dignity of the nation."
Duda added that thanks to such values, Poles "ultimately won, overthrew the red dictatorship and rebuilt a free Poland," the PAP news agency reported.
The president stated that the memory of December 1970 would hopefully serve as an "obligation to strengthen our sovereign state, based on solidarity."
The December 1970 workers’ massacre
In December 1970, drastic price rises led to massive, more than weeklong protests in Gdynia as well as Gdańsk and Szczecin in northern Poland, triggering one of the most brutal crackdowns of the communist era.
Forty-four people were killed and more than 1,100 injured after police and soldiers opened fire on protesters, who also demanded a change of government and freedom of speech.
December 17, 1970, so-called "Black Thursday," marked the worst day of the crackdown.
Solidarity, the first independent trade union in a Warsaw Pact country, was born in August 1980 at a Gdańsk shipyard.
It played a key role in bringing about the collapse of communist rule in Poland in 1989.
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Source: PAP, Institute of National Remembrance IPN, New Eastern Europe