MOSCOW – The law banning American adoptions brought out the biggest crowd of demonstrators in months Sunday as Russians angrily accused their government of playing politics with orphans, depriving them of the opportunity for a decent life.

Many thousands walked through gently falling snow and harsh cold, some carrying posters bearing the names and faces of the 420 members of the Duma, or lower house of parliament, who voted for the ban last month. Only seven voted against it.

The word “shame” was emblazoned across the legislators’ photos, and the protest was organized as the March Against Scoundrels.

The march came after 13 extraordinary months in Russia’s emerging political consciousness. In December 2011, demonstrators unexpectedly began rallying for fair elections, charging that the vote for the Duma that month had been distorted by widespread fraud in favor of President Vladimir Putin’s United Russia party. The authorities have fought back with repressive laws and a robust anti-Americanism.

Although leaders of the opposition joined Sunday’s march, it was cast as a civic rather than political event.

“I’m against this anti-orphan law,” said Yevgeny Skvortsov, a 22-year-old student. “Children shouldn’t be caught in bureaucratic games.”

The adoption ban was passed in retaliation for U.S. enactment of the Magnitsky Act in early December, which imposes visa and financial restrictions on corrupt Russians. The law infuriated Putin and his government, but many Russians approved of it because they saw it as aimed at crooked officials rather than ordinary citizens.

“I’m very grateful to the American people for the Magnitsky law,” said Georgy Didenko, who journeyed three hours by train from the city of Tver to join the protest. “You saved the honor of the Russian people with this law. We didn’t – you did.”