"Dissent is a right in any democracy and it is entirely disproportionate that [the punk band's members] face seven years in jail for what we consider a preposterous charge of 'hooliganism motivated by religious hatred,'" read a letter from the musicians, published by British media on Thursday.
The signatories also include Martha Wainwright, Neil Tennant of Pet Shop Boys, former The Smiths member Johnny Marr, Kate Nash, Alex Kapronos of Franz Ferdinand and others.
The letter charges that Pussy Riot members Nadezhda Tolokonnikova, Mariya Alekhina and Yekaterina Samutsevich were engaged in legitimate protest in February when they performed what the trio described as a "punk prayer" — a protest song blasting Russian President Vladimir Putin and the Russian Orthodox Church — in Moscow's Christ the Saviour Cathedral.
"We believe firmly that it is the role of the artist to make legitimate political protest and fight for freedom of speech," the letter read.
The supporters also voiced concern "about recent reports that food is being withheld from them and that they have appeared in court in a cage."
Putin is currently in London to meet with British Prime Minister David Cameron. A noted sportsman, Putin is also expected to attend some Olympic matches.
"As he visits the United Kingdom this week, we ask President Putin to ensure these three women receive a fair hearing," the letter says.
This week, Tolokonnikova, Alekhina and Samutsevich entered a not guilty plea in their trial. In custody since February, the trio faces up to seven years in prison if convicted. Their protest came amid a wave of rallies decrying this year's election results and demonstrations blasting Putin.