From left: Band members Nadezhda Tolokonnikova, Maria Alyokhina and Yekaterina Samutsevich appear in court Monday.

Story highlights

Three members of Pussy Riot are on trial, facing a potential seven-year sentence

They sang an anti-Putin song in Moscow's Christ Savior Cathedral

Alex Kapranos of Franz Ferdinand and Pete Townshend of The Who want them set free

Their open letter comes as Vladimir Putin visits London

London CNN  — 

Music stars including Pete Townshend of The Who, Alex Kapranos of Franz Ferdinand and Corinne Bailey Rae called on Russia to free three members of the punk rock band Pussy Riot, who are on trial in Moscow on hooliganism charges.

The musicians said the charge was “preposterous,” arguing that artists “make legitimate political protest and fight for freedom of speech.”

The Pussy Riot members went on trial Monday, charged with hooliganism after performing a song criticizing President Vladimir Putin in one of Moscow’s grandest cathedrals, Russia’s state news agency reported.

“Mother Mary please drive Putin away,” the band screamed, their faces covered in neon masks, inside Christ Savior Cathedral in February. Three were arrested soon after.

The charge carries a potential seven-year sentence.

Putin is visiting London on Thursday, Pussy Riot’s celebrity backers noted as they urged him to “ensure these three women receive a fair trial.”

“We are especially concerned about recent reports that food is being withheld from them and that they have appeared in court in a cage,” their supporters said in a letter to the Times of London.

Nadezhda Tolokonnikova, 23, Maria Alyokhina, 24, and Yekaterina Samutsevich, 29, grinned at cameras and waved their handcuffed arms behind their backs Monday as police brought them from a van into the court.

They appeared in court in an enclosure that forced them to bend down to speak through small window to be heard.

The women apologized to Orthodox Christian believers if they felt they had been insulted, state news agency RIA-Novosti reported. The trial is taking place at the Khamovnichesky Court, the agency said.

Read more: Jailed punk band Pussy Riot pushes free speech limits in Russia

Amnesty International said Monday the trial “never should have taken place.”

John Dalhuisen of Amnesty said the singers had been making “a legitimate protest – this is not a criminal offense. They must be released immediately.”

“They dared to attack the two pillars of modern Russian establishment – the Kremlin and the Orthodox Church. While many may have found their act offensive, the sentence of up to seven years in prison they may expect on the charges of hooliganism is wildly out of all proportion,” he said.

Pussy Riot specializes in sudden, often illegal public performances, including one in Moscow’s Red Square.

The punk prayer was inspired by the women’s anger about the relationship between the Russian government and the Orthodox Church, according to their manager, Tolokonnikova’s husband.

The Orthodox leader Patriarch Kyril has been widely reported as saying Putin’s years in power have been a miracle from God.

The band’s behavior in one of Russia’s most sacred cathedrals has outraged many of the country’s faithful.

“This is a disgusting thing to do,” one woman told CNN.

“They should go to jail,” said another. “A year or two. Let them think about their behavior.”

But even some of those who were offended believe the women should not be in jail.

“If necessary, God will punish them,” said one man. “It must be not be cruel punishment.”

CNN’s Phil Black and Alla Eshchenko contributed to this report.