Jarvis Cocker, Pete Townshend and other musicians have called on the Russian President Vladimir Putin to ensure the members of Russian punk band Pussy Riot are given a fair trial in Moscow.
Nadezhda Tolokonnikova, Mariya Alekhina and Yekaterina Samutsevich were taken into custody in February after singing a protest song against Putin in Moscow.
In a letter to The Times, the musicians said theirs was "a legitimate protest" and called on Putin - in London this week for the Olympics - to ensure they receive "a fair hearing".
Martha Wainwright, Neil Tennant of Pet Shop Boys and Johnny Marr, formerly of The Smiths, are among the other signatories.
The Pussy Riot protest, which took place at Moscow's Christ the Saviour Cathedral, outraged the Russian Orthodox Church, which accused them of blasphemy.
Supporters of the trio say the case reflects the state's growing intolerance of government opponents and that they have been mistreated since being detained.
One of the band's members received medical treatment in court on Wednesday during the trio's trial on charges of hooliganism motivated by religious hatred or hostility.
The three pleaded not guilty on Monday but apologised for the offence their performance had caused. If convicted they face up to seven years in prison.
In their letter, the musicians said they were "extremely concerned" over how Pussy Riot have been treated and called for their release.
"We are especially concerned about recent reports that food is being withheld from them and that they have appeared in court in a cage," they continue.
"We believe firmly that it is the role of the artist to make legitimate political protest and fight for freedom of speech.
"As he visits the United Kingdom this week, we ask President Putin to ensure these three women receive a fair hearing."
Kate Nash, Corinne Bailey Rae and Alex Kapronos of Franz Ferdinand are also among the signatories, alongside the bands Cornershop and The Joy Formidable.