The U.S. visa of Bill Browder, a prominent critic of the Kremlin, was revoked after Moscow exploited a loophole to place him on the Interpol wanted list, the financier revealed Saturday.

The move against the U.S.-born British citizen was labeled farcical, and prompted immediate calls for the U.S. to overturn the decision.

“This is outrageous,” Michael McFaul, a former U.S. ambassador to Russia, tweeted Sunday, urging President Donald Trump to “not join Putin’s campaign” against the human rights champion.

Browder has led the push for countries to adopt “Magnitsky Act”-type laws that empower governments to freeze assets of Russian figures linked to human rights violations.

Last week, Canada became the fourth country after the U.S., Britain, and Estonia to pass a Magnitsky Act, leading Vladimir Putin to accuse Browder of “illegal activity.”

Browder, who testified at a congressional hearing in July on Russian election interference, said he was made aware that Russia had successfully placed him on Interpol’s list after he received an email from the U.S. Department of Homeland Security Saturday informing him his “global entry status” had been revoked.

Four previous attempts by Russia to place Browder on the list failed; on each occasion Interpol said the move was politically motivated.

The fifth time, Moscow used a loophole in the process that allows states to unilaterally place individuals on the database through a “diffusion notice,” effectively bypassing Interpol scrutiny, Browder told EU Observer on Sunday.

“This is a loophole that’s clearly being abused and needs to be closed,” he said. “It’s clear that countries like Russia are serial abusers of Interpol and shouldn’t be treated the same as legitimate states.”

Last year, the Council of Europe criticized Russia’s efforts to arrest Browder through Interpol as “abuses” of the system.

Once the largest foreign-portfolio investor in Russia, Browder began his campaign against the Kremlin after his accountant, Sergei Magnitsky, uncovered a $230 million scam by Russian tax officials.

He was jailed and died in prison in 2009 after being denied medical care.

The latest charges against Browder from Russian prosecutors allege he colluded with British intelligence to kill Magnitsky by convincing prison doctors to deny him treatment.

Browder responded to the allegations in a tweet, saying they “couldn’t get more absurd.”