Supporters of Russian opposition leader Alexei Navalny are expected to descend on Moscow city centre for an unauthorised protest against fraud.
Mr Navalny got permission to hold the rally at another location but said he had moved it after authorities tried to “humiliate” protesters.
The prosecutor’s office has warned police will take action against any unauthorised demonstrations.
Small protests are being reported in cities in the Russian far east.
The last wave of protests led by Mr Navalny ended with hundreds arrested.
Those protests were the largest since 2012, drawing thousands of people – including many teenagers – to rallies nationwide, angered by a report Mr Navalny published accusing Prime Minister Dmitry Medvedev of corruption.