At least 200,000 people attended a mass rally in Prague against Czech Prime Minister Andrej Babis on the eve of the 30th anniversary of the Velvet Revolution.
Organisers of the protest said more people attended than had previously done at a similar event in June, which had then been considered the largest of its kind since the fall of Communism in 1989.
They estimated that 300,000 of the country's 10.7 million inhabitants had joined the rally. Police put the turnout at around 200,000.
Sunday marks 30 years since peaceful mass protests led to the downfall of Czechoslovakia's totalitarian regime.
"Thirty years after the Velvet Revolution, we have little reason for optimism," said the activist group Milion Chvilek, or Million Moments for Democracy. "Justice and the public media are in jeopardy."
The manifesto for the rally demanded that politicians be free of conflict of interest and respect the country's laws and institutions.
Babis, a Slovak-born billionaire, has been investigated over a €2 million EU subsidy paid to a farm and convention centre that is now part of his giant Agrofert business, one of the country's largest private employers. He insists the site was owned by family members at the time of the subsidy, making it eligible, and has dismissed complaints about him as "fake news".
Czech police recommended that Babis be charged, but the country’s justice minister resigned the next day and the case has been dropped.
Separately, a European Commission audit ruled that Babis has a conflict of interest as a politician and entrepreneur. More than 430,000 people have signed a Million Moments petition calling on him to resign.
But despite his controversy, Babis' ANO movement still remains a dominant political force in the Czech Republic, winning the recent European elections in May.