A group of leading Russian lawyers on Tuesday asked the country’s highest court to declare a law banning criticism of the Russian armed forces unconstitutional, in a rare display of opposition against draconian censorship measures imposed by the Kremlin in the wake of the invasion of Ukraine.

The complaint, filed by three lawyers and supported by 10 more, most of whom are still in Russia, asked the Constitutional Court to repeal the measure, which has emerged as the Kremlin’s most effective tool for stifling antiwar dissent in the country.

“This law was passed with only one goal — to suppress antiwar activism,” said Violetta Fitsner, a lawyer with OVD-Info, a Russian rights group, and one of the authors of the complaint.

The law and related censorship measures have virtually silenced debate in Russia. Since the invasion, thousands of anti-Kremlin activists, journalists, and other professionals have left the country.

Many others, including lawyers, have been arrested and prosecuted. But some have stayed and continued their work.