Russia's opposition is preparing to hold a major anti-government rally in Moscow despite government orders for several protest leaders to appear for questioning as the demonstration gets under way.

Tuesday's rally is the first to be called by the opposition since Vladimir Putin returned to the Russian presidency last month and began tightening a government crackdown on dissent. The last big opposition rally in the Russian capital turned violent on the eve of Mr. Putin's May 7 inauguration, with police beating protesters, some of whom threw bottles and stones.

Russian police raided the homes of four prominent protest leaders on Monday as part of an investigation into the May 6 riot. Authorities also summoned the four for questioning by investigators on Tuesday morning, one hour before the new rally was due to start.

Russia's Interfax news agency said dissidents Alexei Navalny, Ilya Yashin and Ksenia Sobchak appeared at the investigation office as ordered, but the location of the fourth dissident, Sergei Udaltsov, was not immediately known.

Opposition activists denounced the police action and vowed to go ahead with Tuesday's protest, timed to coincide with the Russia Day national holiday. Russian Internet users angered by the crackdown also likened it to the repression of Soviet dictator Josef Stalin, posting Twitter messages mentioning 1937, the year of his greatest repression.

In another move to pressure the opposition, Mr. Putin signed a law on Friday that dramatically increases fines on people who participate in unauthorized protest actions. Under the law protesters held responsible for physical injury or property damage face penalties of up to $9,000, equivalent to the country's average annual salary.

Russian authorities granted permission for Tuesday's march from Pushkin Square to Sakharov Avenue, but organizers expressed concern that minor violations of their permit would give security forces a pretext to make arrests.

In Monday's raids on the protest leaders' homes, the activists said police barged into their apartments early in the morning, ransacked their belongings and took away computers and other possessions.

U.S. State Department spokeswoman Victoria Nuland criticized the raids, saying Washington is “deeply concerned by the apparent harassment” of the opposition leaders on the eve of planned demonstrations and the “arbitrary use of law enforcement.”

Mr. Putin was elected to a record third presidential term in March. He served two terms as president from 2000 to 2008 before switching to the role of prime minister due to constitutional limits on consecutive presidential terms.

A subsequent constitutional amendment extended the term of a Russian president to two consecutive six-year periods, meaning Mr. Putin could stay in power until 2024.