MOSCOW (AP) — Russian opposition leaders say they have been questioned again by investigators a day after they helped organize the largest protest since Vladimir Putin’s return to the presidency.

Anti-corruption whistleblower Alexei Navalny and leftist leader Sergei Udaltsov tweeted Wednesday that they have been summoned for questioning to Russia’s Investigative Committee for the second day in a row over a May rally in which protesters clashed with riot police.

Tens of thousands marched peacefully Tuesday in Moscow despite heavy police presence and a repressive new bill that introduced heavy penalties for taking part in unauthorized rallies.

On Monday, police searched top opposition activists’ apartments, carting away computers, safes, cellphones and other personal items.