OVD-Info joins the Mediazona website and the human-rights project Zona Prava on Russia's blacklist of critical media organisations.
Russia has designated a prominent protest monitoring group and 22 individuals as "foreign agents" in the latest move in what critics say is a broad crackdown on independent media.
OVD-Info, which played a major role in documenting anti-Kremlin demonstrations, is the latest to join the Mediazona website and the human-rights project Zona Prava on Russia's blacklist of critical media organisations.
Russia's Justice Ministry did not offer any explanation for the move.
OVD-Info monitors the activities of law enforcement organisations and offers legal support to those detained by the police. Its cofounder, Grigory Okhotin, said the organisation will continue to work, adding the latest move "can't stop us at all".
"What kind of particular difficulties will it bring? We'll see! But such a label never makes you feel better," Okhotin added.
"This is not a surprise, we associate it with a campaign of pressure on independent organisations and the media. This did not begin today. It’s curious that it happened at the height of the public campaign to abolish the foreign agent legislation, in which OVD-Info was one of the key initiators."
Earlier this month, 20 independent media outlets signed a letter to President Vladimir Putin asking to cancel the foreign agent list and change the legislation.
Russia's foreign agent legislation was adopted in 2012 and has been modified repeatedly.
It requires NGOs that receive foreign assistance and that the government deems to be engaged in political activity to be registered, to identify themselves as "foreign agents", a term that carries negative Soviet-era connotations, and to declare their status in disclaimers on their output.
Human Rights Watch has condemned Russia’s "foreign agent" laws, calling them "another repressive tool the government can use to harass independent groups."