MOSCOW - Russian authorities say they intend to add an opposition-run anti-corruption foundation to a list of so-called "foreign agents" operating in the country - potentially curtailing the operations of one of the Kremlin's fiercest critics.

In a statement released Wednesday, Russia's Justice Ministry said an audit of the Anti-Corruption Foundation - a non-governmental organization run by opposition leader Alexey Navalny - showed the organization was receiving foreign funding to maintain its operations.

The move puts the group, commonly known by its Russian acronym FBK, afoul of Russia's so-called "foreign agents" law - a controversial 2012 measure the Kremlin says is necessary to protect Russian sovereignty and that civil society leaders argue tars NGOs as traitors and spies.

Formally, the designation opens up the FBK to increased scrutiny by authorities - as well as fines and possible suspension of its operations.

While the ministry statement provided no details on its audit, an Interfax news agency report said regulators had found two undeclared foreign donations to the FBK - one from the U.S. and another from Spain.

Their total: just over $2,000.

FBK members rejected the foreign agent charge outright, arguing the organization had always relied on local "crowdfunding" to maintain its work.

"The foundation is sponsored inclusively by citizens of Russia, by you," wrote FBK Director Ivan Zhadanov in a Facebook post.

"This is simply an attempt to strangle the FBK," added Zhadanov.

The group's founder, opposition leader Alexey Navalny, went further - arguing the move reflected the foundation's growing influence thanks to a series of video investigations targeting corruption by Kremlin insiders close to Russian President Vladimir Putin.

"Putin is terribly afraid of the FBK," wrote Navalny in a post on Twitter. "He can only rely on thieves, bribe takers, and corruptioneers.

"We expose corruption" added Navalny, "and we won't stop no matter what."

An NGO in the crosshairs

The announcement comes amid an intensifying assault against the FBK with overt political overtones.

A longtime thorn in the Kremlin's side, the FBK's troubles began in earnest again this summer.

After opposition candidates - including members of the FBK - were banned from local Moscow elections en masse, the group worked to organize street protests in response.

The result: a series of mostly peaceful demonstrations that saw over 2,500 arrests - many at the hands of truncheon-wielding police and aggressive OMON (federal government) riot police security forces.

Next, authorities launched an investigation into money laundering by the FBK - accusing the organization's members of over $15 million in illicit transactions. Coordinated raids of FBK offices across the country ensued.

At the time, Navalny insisted the raids were prompted by an FBK plan called "smart voting" - an election tactic that coordinated voter anger around candidates who had managed to clear registration barriers.

The strategy was credited with aiding significant losses for pro-Kremlin candidates in Moscow local elections.

FBK members say they plan to expand the strategy in regional political races in 2020 - a move that observers say may have prompted renewed efforts to cripple the organization.

Indeed, the FBK has most recently drawn authorities' ire in the form of court fines.

This week, Moscow police announced they would sue Navalny and other key FBK members for $300,000 in damages - a sum intended to cover expenses incurred by security forces while policing the rallies.

A Moscow restaurant and several other city services have piled on with similar lawsuits.

Now faced with the prospect of the new foreign agent label, Navalny and other FBK members took to social media to plead for renewed donations nationwide.

Throughout the day, the requests ricocheted around the internet, prompting reaction from pro-Kremlin voices online as well as public expressions of support.

"I haven't done that in a while," wrote user @DaniilKen in a post on Twitter that showed a screenshot of a money transfer to the FBK. "But it was hard not to respond to the Justice Ministry."

Just how many more Russians might follow now remains the key question going forward.