ON FEB. 21 IN MOSCOW, five young women, dressed in neon spandex and colorful ski masks, stood in front of the altar in the gilded Cathedral of Christ the Savior, headquarters for the patriarchate of the Russian Orthodox Church.

To show disrespect was the women’s intent. They are Pussy Riot, a female punk band whose work is broadly anti-authoritarian and feminist. They had been popping up in recent months with protest performances, some aimed at President Vladimir Putin. In the cathedral, they danced, hopped and uttered a few lines of a “punk-prayer” with the refrain “Our Lady, chase Putin out.”

The stunt lasted about 30 seconds before they were ejected, but a subsequent video, with music and more lyrics spliced in, was distributed online. Three of the women were detained in March and have been sitting in prison ever since; their incarceration was just extended for six months. They are charged with “hooliganism” — but the case is about much more.

The person who appears to have been most offended was Mr. Putin, who has faced large street demonstrations against his rule in recent months. The incarceration of Pussy Riot can only be interpreted as an attempt to make an example out of Nadezhda Tolokonnikova, 23; Maria Alekhina, 24; and Ekaterina Samutsevich, 29. Two are mothers of young children.

Some 200 prominent Russian culture and arts figures signed a letter expressing outrage, and 42,000 people have added signatures. Certainly, Russians are entitled to be offended or delighted by the cathedral antics. A brief arrest or citation might have been appropriate for the stunt, but months or years behind bars is grossly excessive.

From their cell, the band sent a handwritten letter to friends and supporters on Thursday. “We’d like to stress that we do not support violence, we have no grudges against anyone, our laughter is in some sense laughter through tears, and our sarcasm is a reaction to judicial lawlessness,” they wrote. While grateful for public support, they acknowledged, “the harshness and rudeness of our opponents is hard to understand even now.”

They go on trial Monday, facing up to seven years in prison, ridiculous for a prank. Mr. Putin ought to free the judicial system to punish the real lawlessness and corruption around him.