Falk, 95, is a longtime critic of the Israeli regime’s abuses against Palestinians.
He said Canadian security officials claimed he and his wife, legal scholar Hilal Elver, posed “a danger to the national security of Canada.”
The incident has triggered anger among Canadian human rights groups.
Corey Balsam, national coordinator at Independent Jewish Voices-Canada, said:
“We need answers – and from the highest levels of government.”
Canadian authorities have not publicly addressed the questioning.
But the office of Public Safety Minister Gary Anandasangaree acknowledged the case.
A spokesperson, Simon Lafortune, said border agencies must follow national-security protocols but added the minister asked the Canada Border Services Agency (CBSA) for “more specific details on how this particular incident occurred.”
Falk told Al Jazeera that officials questioned him and Elver about their work on Israel, Gaza, and genocide.
He said they were also asked about their participation in an Ottawa event examining Canada’s role in the Israeli regime’s war on Gaza, which a UN inquiry and multiple rights groups describe as genocide.
After more than four hours, the couple — both US citizens — were permitted to enter Canada to attend the Palestine Tribunal on Canadian Responsibility.
Alex Paterson of Canadians for Justice and Peace in the Middle East called the treatment “patently ridiculous.”
He said the government “wanted to hamper the tribunal’s work and try and keep Canadian complicity in Israel’s genocide … in the shadows.”
He added that Ottawa “has been trying to avoid questions of its complicity in arming the genocide.”
Since the Israeli regime began its genocidal war on Gaza in October 2023, Canadian rights advocates have pushed the government to pressure Israel to halt the assault.
Those calls intensified as Israel’s military atrocities and aid restrictions have killed tens of thousands and driven Gaza into humanitarian collapse.
Last year, Canada suspended some weapons export permits to Israel.
Prime Minister Mark Carney, in office since March, criticized Israel’s blockade of aid to Gaza and rising Israeli military and settler violence in the occupied West Bank.
In September, Canada joined several allies in recognizing an independent Palestinian state.
But researchers say loopholes in Canada’s export system allow Canadian-made weapons to continue reaching Israel, often through the United States.
They argue Canada should take stronger steps to halt Israeli attacks in Gaza and the West Bank and support accountability efforts at the International Criminal Court.
Falk said his interrogation reflects a broader attempt to silence criticism of the Israeli regime’s actions in Gaza.
“It suggests a climate of governmental insecurity, I think, to try to clamp down on dissident voices,” he said.
Al Jazeera asked multiple Canadian agencies whether Ottawa considers Falk a national-security threat.
A CBSA spokesperson said the agency cannot comment on specific cases.
The spokesperson, Rebecca Purdy, said secondary inspections are routine and “travelers referred to secondary inspection are not being ‘detained.’”
She added that foreign nationals may face extended questioning to determine admissibility.
Global Affairs Canada has not responded to Al Jazeera’s request for comment.
Balsam said treating someone like Falk as a security threat signals that “none of us are safe from the suppression of dissent and crackdown on voices that are critical of the Israeli regime.”
He said Canadians deserve an explanation for an incident that “casts a chill for all Canadians that are speaking out about human rights in general and Palestine in particular.”