AFTER VLADIMIR PUTIN announced his plans to return to the Russian presidency last September, discontent erupted in Moscow and other cities. Tens of thousands of people who had been indifferent to politics for many years spontaneously turned out at rallies, expressing disapproval of Mr. Putin’s job switch with then-president Dmitry Medvedev and the blatant irregularities in the December parliamentary elections.

The Russian parliament, which is under Mr. Putin’s thumb, this week gave the demonstrators something to think about before they return to the streets. Both chambers passed legislation that would sharply boost fines for people found guilty of violating the public order, up to a maximum of 300,000 rubles, or about $9,150. The previous maximum had been 5,000 rubles. The maximum fine for organizations would go up to 1 million rubles, or about $30,500.

The legislation is expected to be signed by Mr. Putin, and the Kremlin seems eager to have it in place before protests planned for next week. While it is a common practice to have rules and procedures for public protests, this legislation seems to be crude overkill, intended to frighten demonstrators from returning to the squares and boulevards that have seen some of the most vibrant expressions of Russian civil society in two decades.

The bill was written with “extremely vague” definitions that could be used for “arbitrary” detention by the police, according to Mikhail Fedotov, head of the presidential council for development of civil society and human rights. For example, he said, even a crowd gathered outside a theater box office at intermission might be vulnerable.

The legislation runs counter to Russia’s constitution, which guarantees the right to peaceful assembly. There was a glint of resistance to the legislation in the lower house of parliament, the State Duma, where some critics of the bill attempted to drag out consideration through a form of a filibuster, offering hundreds of amendments, but it eventually passed.

The episode offers fresh evidence that Mr. Putin feels deeply threatened by the protests. Although many analysts in Russia have expressed hope that a more open and competitive political system might grow out of the demonstrations, Mr. Putin shows no sign of considering it. He endorsed the new legislation, saying, “We must shield our people from radical actions.” How radical? In some of the recent protests, participants have held aloft placards saying, “Russia without Putin!” Now, Mr. Putin is saying he wants a Russia without them.