Morawiecki told reporters after holding talks in Warsaw with Slovenian Prime Minister Janez Janša that Nord Stream 2 "is a German-Russian project that destabilizes Europe and reduces Europe's security."
He added: "We are calling on Germany to give up this project, to stop further [contributing to] destabilization in this part of Europe, because this may be very dangerous for the European Union and for many countries in this region."
Nord Stream 2, designed to double the capacity of the existing Nord Stream undersea gas pipeline, is expected to send around 55 billion cubic metres of Russian natural gas a year directly to Germany under the Baltic Sea while bypassing the Baltic states, Poland and Ukraine.
Poland has strongly criticised the gas link amid concerns that the pipeline will make the European Union more dependent on Russian gas.
During their meeting in Warsaw, Morawiecki and Janša discussed Slovenia's priorities as it prepares to take over the rotating presidency of the European Union on July 1.
US Secretary of State Antony Blinken warned in March that the Nord Stream 2 pipeline, which is almost complete, could undermine the interests of a number of NATO allies, including Poland.
Speaking on a visit to NATO headquarters in Brussels, Blinken said US President Joe Biden “believes the pipeline is a bad idea, bad for Europe, bad for the United States.”