The legislation, signed into law earlier this month by Russian President Vladimir Putin, had already drawn scorn from critics in and outside of Russia. Known as the "Yarovaya Law," the measure includes new police and counterterrorism measures that directly echo the sweeping powers wielded by the KGB to stifle dissent and repress opposition activists throughout the Soviet era.

But one largely overlooked aspect of the law is garnering new scrutiny and worry: tight restrictions on the activities of religious groups, particularly smaller denominations.

The new restrictions "will make it easier for Russian authorities to repress religious communities, stifle peaceful dissent, and detain and imprison people," said Thomas J. Reese, who heads the U.S. Commission on International Religious Freedom, a federal government agency that monitors religious expression around the world.

"Neither these measures nor the currently existing antiextremism law meet international human rights and religious freedom standards," he said in statement released last week.