Historian Jan Grabowski, of the University of Ottawa in Canada, told The Associated Press he brought a lawsuit on Thursday against the Polish League Against Defamation, an organization allied with Poland's conservative ruling party.
The head of the organization, Maciej Swirski, said he had not received formal notification of the suit yet and would only comment after he does. Last year, the league said Grabowski "falsifies the history of Poland, proclaiming the thesis that Poles are complicit in the extermination of Jews."
"During World War II, due to the demoralizing circumstances and German actions, it is true that vile-acting individuals could be found among Poles and Jews alike," the group wrote in a statement signed by dozens of Polish academics. "Yet, we should remember that the objective of the Germans was also to 'eradicate the Polish nation' and 'completely destroy Poland.'"
The anti-defamation organization has been part of a broader effort under the government of the populist Law and Justice party to challenge research on Polish participation in the killing of Jews by Nazi Germany. Poland was under German occupation during World War II.
"What is important, from my point of view, is that the militant nationalists who nowadays hold sway in Poland be warned that they will be held to account, that they are wrong if they think that their outrageous statements and slanders will go unnoticed," Grabowski, who was born and attended university in Warsaw, told the AP.
Official efforts under the Law and Justice government have included promoting the memory of the Polish gentiles who sheltered Jews during the war. Scholars who research Polish violence against Jews have faced censure and prosecution.
The issue came under international scrutiny earlier this year when Polish lawmakers voted to make it illegal to blame the nation for Holocaust crimes. The law has since been amended to remove prison as a possible punishment for violators, though individuals can still be tried and fined. The measure created a rift with Israel and was also condemned by the U.S.
Also Friday, the Polish ambassador to Germany, Andrzej Przylebski, accused Germans of frequently reducing World War II to the Holocaust "as if Adolf Hitler was primarily or exclusively concerned with the murder of European Jews."
At a Berlin conference attended by the German foreign minister, Przylebski said Polish victims "are almost completely forgotten or downplayed," according to a report from the Wirtualna Polska news portal.
Grabowski's "Hunt for the Jews: Betrayal and Murder in German-Occupied Poland" documents the involvement of Poles in one rural area in finding and killing Jews who had escaped from ghettos and were trying to survive by hiding among gentiles. It was awarded the 2014 Yad Vashem International Book Prize for Holocaust Research.
The book also sparked heated debates, and the scholar says he received death threats after its publication. After a German newspaper reviewed the book favorably, a far-right Polish website ran an article with a photograph of the Nazi propaganda minister Joseph Goebbels. The headline was "Sieg Heil, Herr Grabowski, Three Times Sieg Heil."
Grabowski successfully sued for libel.