Russian police have detained some 20 people outside the country's parliament who were protesting a bill that would dramatically raise fines for holding unsanctioned rallies.

The bill, introduced by the ruling United Russia party, would raise maximum fines for joining illegal rallies from $30 to $9,000. The party originally proposed an increase to at least $31,000.

The Kremlin-controlled parliament has begun debating amendments to the bill and is expected to approve it this week. Opposition lawmakers have proposed more than 350 amendments in an effort to delay passage of the measure.

Critics say the bill would increase tensions in Russian society and make it very difficult to hold protests.

The bill was introduced after activists held mass protests against the possible 12-year rule of Russian President Vladimir Putin, a scenario that many Russians find unsettling.

Mr. Putin was elected to a record third presidential term with 64 percent of the vote in March. He served as president from 2000 to 2008, but term limits prevented him from running for a third straight term. He then became prime minister under former president Dmitry Medvedev.

A constitutional amendment has extended the president's time in office to two consecutive six-year terms, meaning Mr. Putin could stay in power until 2024.