Academics have rallied to the defence of one of the world’s leading Holocaust historians after reports that Poland intends to strip him of a national honour because he claimed that Poles were complicit in Nazi war crimes.

Princeton University professor Jan Tomasz Gross, 69, was awarded the Order of Merit of the Republic of Poland in 1996. He is best known for his 2001 book Neighbors, which describes in graphic detail the 1941 massacre by Polish villagers of up to 1,600 Jewish men, women and children. The book inspired Aftermath (Pokłosie), a 2012 film directed by Władysław Pasikowski.

A scene from the 2012 film Aftermath, based on Gross’s book. Photograph: Menemsha Films/Everett/Rex Shutterstock

The move against the historian comes as the nationalist Law and Justice government, elected in 2015, comes under European scrutiny for law changes that, critics say, threaten democracy. President Andrzej Duda signed into law a controversial move bringing the attorney general under the control of the justice ministry. Critics say this will put political pressure on the judiciary.

Intellectuals who in the past few days have signed two open letters in Gross’s defence say the Law and Justice government wants to rewrite history, expunging any suggestion of Polish complicity in past horrors.

“The government says Gross is unpatriotic. But he is a patriot who looks at both the darker and lighter periods in Polish history,’’ said University of Ottawa history professor Jan Grabowski, who is among 30 signatories of the first letter, published last week.

Professor Jan Tomasz Gross, whose book “Neighbors” tells of the massacre of Jews in Jedwabne. Photograph: Czarek Sokołowski/AP

Gross was born in Poland but left the country in 1969 after an antisemitic purge on dissidents. Last September, in an article published in Germany’s Die Welt newspaper, he lamented eastern European countries’ reluctance to accept refugees and asserted that Poles killed more Jews than they did Nazis during the second world war. Prosecutors in Warsaw decided to investigate whether Gross had broken laws prohibiting the defamation of Poland.

“Gross is controversial, but it is stupid and harmful to consider removing his award,’’ said Dariusz Stola, director of Warsaw’s Polin Museum of the History of Polish Jews, who signed the second open letter, submitted to the Polish Press Agency on Friday.

Stola said Duda should bear in mind the broad context of Gross’s work, which included valuable studies of the German and Russian occupations of Poland. “He was awarded the Order of Merit for his scholarly work but also for his contribution, while in exile, to the democratic transition,’’ said Stola. “These are achievements you cannot take away.”

Gross is currently on sabbatical leave from Princeton and did not respond to a request for comment from the Observer. But at a recent talk, posted online by the University of Haifa last week, he described his work as “a confrontation with ghosts in the consciousness of Polish society’’. He said most Poles were still not aware that 3.5 million Jews had died in Nazi death camps. The Law and Justice government was, he said, “vested in martyrology’’.

He said to the students: “Historians write about what happened. What the consequences are is not your responsibility or business. Speaking and knowing the truth is a necessary step towards clarifying and setting relationships between groups on a path of mutual understanding.’’

Agata Bielik-Robson, professor of Jewish Studies at Nottingham University, said: “Gross is one of the world’s leading Holocaust historians. Any normal liberal democracy has to have a voice of inner criticism, speaking in the name of minorities and different interests. Gross is one of those voices for Poland.’’

Bielik-Robson, who is Polish and also signed the open letters, added: “Law and Justice want to eliminate voices like his, to produce a uniform historical perspective. The trend is deeply worrying.’’

An announcement on Gross’s Order of Merit is expected soon. Małgorzata Sadurska, a member of the presidential staff, told the state-run TV station TVP last Tuesday that 2,000 letters had been sent to the presidency calling for the historian to be stripped of his honour. She said Duda had requested an opinion from the Polish foreign ministry. The ministry, in turn, said its statement was ready and has been submitted to President Duda.