Supporters of Russian opposition leader Alexei Navalny are expected to descend on Moscow city centre for an unauthorised protest against fraud.
Mr Navalny was given 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 that police will take action against any unauthorised demonstrations.
There have been several arrests at protests in the east of the country. At least ten people were detained at a rally in the city of Vladivostok.
Four people were also detained in the city of Blagoveshchensk and at least one other in Kazan, as small protests got under way in cities east of Moscow ahead of nationwide demonstrations.
Mr Navalny is due to attend the rally in central Moscow later on Monday. He was earlier granted permission to hold a rally at Sakharova Avenue but changed the location on the eve of the demonstration to Tverskaya Street, near the Kremlin.
One of the groups participating in the Moscow rally, which is over government plans to demolish Soviet-era apartment blocks in the city, said it would hold its protest on Sakharova Avenue as planned.
Permission has been granted for demonstrations in 169 locations across the country, some of which will be broadcast live on the Navalny Live YouTube channel. The main rallies are expected to be in St Petersburg and Moscow.
Despite it being a public holiday in Russia, turnout in Monday's protests has so far been lower than similar rallies led by Mr Navalny in March, which led to hundreds of arrests.
Those protests were the largest since 2012, drawing thousands of people - including many teenagers - to rallies nationwide, angered by a report published by Mr Navalny that accused Prime Minister Dmitry Medvedev of corruption.