Not one to shy away from controversy, Madonna has been known to challenge the establishment.

But now it's her fans asking her to use her powers of persuasion to help fellow musicians in Russia, the punk girl band Pussy Riot.

The three women face up to seven years in prison.

It stems from this incident, the band went into Moscow's Christ the Saviour Cathedral, ascended the altar and called on the Virgin Mary to "throw Putin out!"

At Madonna's concert in Warsaw on Monday (August 1), fans called on the Material Girl to speak out against what they say is an injustice.

SOUNDBITE: Madonna Fan, From Kaliningrad, Russia, Anastasia Jakubowska, saying (Russian): (APPROXIMATE TRANSLATION)

"I hope that Madonna who will come to perform in Moscow, that she will be able to help, so that the verdict won't be very harsh, or maybe they will be set free."

SOUNDBITE: Madonna Fan From Katowice, Ola, saying (Polish):

"In my opinion, if she's going to Moscow she can appeal to Putin to help the girls in some way. But it won't work because of Russian politics and the power of Putin."

A number of celebrities have banded together to call on Russian president Vladimir Putin to ensure Pussy Riot get a fair trial in Moscow.

The bands wrote a letter to Britain's Times newspaper, saying they had "a legitimate protest" against Putin, who's currently in London for the Olympics.

Pete Townshend, Neil Tennant of Pet Shop Boys and Johnny Marr formerly of the Smiths, are amongst the signatories.

Madonna's tour is set to arrive in Moscow on August 8, but the world will have to wait to hear whether her voice will join the growing list of the celebrity dissenters.

Cindy Martin, Reuters