Russian deputies debated long and hard on Tuesday over a Kremlin-backed draft anti-protest bill.
In the end, the new law designed to raise fines for orchestrating unauthorised demonstrations was approved, but only after arguing over 400 amendments.
The unease within the Duma was reflected by protesters outside who accuse President Vladimir Putin of smothering dissent.
Opposition leader Sergey Mitrokhin was one of 20 people arrested. He said the new law was so ambiguously written that it would not even allow people to walk down the street, let alone to express political views.
From now on, organisers of unsanctioned protests can be charged up to the equivalent of 39,000 euros – participants 13,000 euros.
Critics say the new law goes against Article 31 of Russia’s constitution, which guarantees freedom of assembly. In the run-up to the Duma debate they held protests on the 31st of each 31-day month calling unsuccessfully for the bill to be rejected.