Thousands of people are expected to take to the streets of Sofia in a seventh consecutive day of protests against Bulgaria's government and top prosecutor on Wednesday amid calls for a general strike.
Demonstrators have also called for them to "resign" amid claims of corruption and criminal connections.
The anti-government protests are the country's biggest in seven years.
Bulgaria's president, Rumen Radev, has backed protesters saying the centre-right government's prime minister, Boyko Borissov, and chief prosecutor Ivan Geshev, should step down.
Geshev last week ordered police to raid the president's office and arrest two of his aides, on suspicion of disclosure of classified documents and influence peddling.
But many saw the move as an attempt to gag the president — a vocal critic of the government.
Radev posted a statement on Facebook and Twitter saying the "protest against the mafia in power is becoming a campaign" and that there "is no power to stop us as long as we are wise and relentless".
Borissov also took to social media to call for peaceful protests, adding: "I respect everyone's right to protest. My door has always been open for dialogue."
"Power is given to us by the people and we exercise it with responsibility," he added.
The US embassy in Sofia backed demonstrators in a statement on Monday, saying "the right to peacefully assemble is a fundamental democratic value" and "no one is above the law" but stopped short of directly referencing their demands that Borissov and Geshev resign.
Although the rallies have been mostly peaceful, there have been occasional clashes and some arrests.