The two jailed members of the art-punk protest band Pussy Riot could be released as early as Thursday as part of a wide-ranging amnesty, according to the group’s lawyer.

Russia’s lower house of parliament this week unanimously approved the amnesty, which is backed by President Vladimir Putin and timed to coincide with the 20th anniversary of Russia’s constitution.

“According to the draft law passed today, my clients will be freed,” lawyer Irina Khrunova told Bloomberg.

Nadezhda Tolokonnikova and Maria Alyokhina (pictured left and centre) are serving two-year sentences for their impromptu protest performance in Moscow’s main cathedral last year.

Tokolonnikova was recently moved from a prison in Mordovia, where she reported “slave-like” conditions, to a jail in the Siberian city of Krasnoyarsk, where she was later hospitalised. Alyokhina is serving her sentence in a prison in the city of Nizhny Novgorod.

Tolokonnikova’s husband, Pyotr Verzilov, told the Guardian the jailed pair were “slightly sceptical” of their possible release. “When you’re living in these conditions it’s hard to think about the Duma passing some bill, and it seems like it could never happen, so it’s a big surprise for them that it does actually seem to be happening.”

The amnesty would also apply to the ‘Greenpeace 30′, crew members of a Greenpeace ship who were detained after their protest against a Russian oil drilling in the Arctic.