Several thousand nationalists rallied in Warsaw on Saturday against a US law on the restitution of Jewish properties seized during the Holocaust, an issue which has surfaced ahead of parliamentary elections later this year.
Far-right supporters who marched from the prime minister's office to the US embassy waved banners reading "No to claims", "Shame" and "Stop 477".
The latter refers to the US Justice for Uncompensated Survivors Today (JUST) Act which requires the US State Department to report to Congress on the progress of countries including Poland on the restitution of Jewish assets seized during World War Two and its aftermath.
Pre-war Poland was a Jewish heartland, with a centuries-old community numbering some 3.2 million, or around 10 percent of the country's population at the time.
Poland's governing right-wing Law and Justice (PiS) party as well as the centrist and liberal opposition have downplayed the law signed by US President Donald Trump in May 2018, insisting that it will have no impact on Poland.
But in the run-up to elections to the European Parliament late this month, an informal alliance of several far-right and nationalist parties and groups joined forces with a farmers' union to campaign against Jewish property restitution.
One of its leaders, Robert Bakiewicz from the far-right National-Radical Camp (ONR) called the 447 law "a threat to Poland and its security since the Jewish organizations are claiming 300 billion dollars (267 billion euros)".
Under the 447 law "the US president must support claims that are illegal, by virtue of the principles of our civilisation, properties without legal heirs belong to the state Treasury," said protester Marek Wawrzyszko.
"This law is a gift to (Russian President) Vladimir Putin," he added, predicting that it will have a detrimental effect on Polish-US relations, which have improved under the Trump administration.
The AGROunia farmers' union, which joined the march, maintains that farmers were worried about possible restitution claims on their land.
The anti-establishment Kukiz'15 movement, which has 26 MPs, as well as an ultra-nationalist coalition set up for the elections to the European Parliament, have each drafted bills formally declaring that Poland will refuse to provide restitution on heirless property.