Russia's Investigative Committee has launched an investigation into the Memorial International human rights organization as the Kremlin widens its crackdown on civil society.
Yan Rachinsky, Memorial's chairman, confirmed on February 5 that he had been called in for questioning.
The Investigative Committee is looking into a complaint against Memorial filed in December by Veterans of Russia, which accuses it of trying to rehabilitate Nazi collaborators.
Memorial International, one of the country's oldest and most respected human rights organizations, has spent decades recording the Soviet government's imprisonment and killing of people on political grounds.
Its list of politically repressed Soviet citizens now exceeds 3 million.
Veterans of Russia claims that list includes 19 people who were Nazi collaborators.
While Memorial said that any database as large as its own "probably" has some mistakes, it largely rejected the claims.
It said 16 of the individuals had been rehabilitated without question by prosecutors, including four who are listed as heroes on the Russian Defense Ministry's website.
It said doubt could only be attributed to three, due to the lack of documentation about their rehabilitation.
Furthermore, it said collaboration did not exclude the fact that an individual was also political repressed, pointing out that some of the people on the list were jailed on trumped-up charges by the Soviet government in the 1930s before later helping the Nazis.
"Illegal repressions, crimes, and exploits are different facts that are not mutually exclusive," it said in a statement at the time.
Russian President Vladimir Putin has sought to sweep under the rug the Soviet Union's abysmal human rights record while trying to unite the country around its victory over Nazi Germany in World War II.
His government has harassed Memorial, other organizations, and academics researching the Soviet Union's criminal past.
Russia's Supreme Court in December ruled to close Memorial, claiming it violated the onerous "foreign agent" law, which is increasingly being used by officials to shutter civil society and media groups.
Memorial has appealed the ruling. Rachinsky said at the time the organization's work would not stop, since parts of it are not legal entities.