The protests are being organized by a coalition of anti-government groups, including chess-champion-turned-politician Garry Kasparov's liberal United Civil Front, radical writer Eduard Limonov's National Bolshevik Party, and the Russian People's Democratic Union, led by former pro-market prime minister Mikhail Kasyanov.
They accuse President Vladimir Putin and his associates of infringing on liberal freedoms and muzzling the opposition.
The initial plan involved a march along Moscow's main thoroughfare, Tverskaya Street, all the way to the Kremlin. But City Hall, citing traffic congestion concerns, banned the opposition from marching downtown and said only a rally will be permitted.
The organizers, however, said they will stick to their original plans because, by law, peaceful protests do not require authorization.
"We have taken additional steps to maintain the format of the action and to avoid outright clashes," Kasparov told a news conference.
Earlier this week, police raided United Civil Front's headquarters in downtown Moscow to search for what they termed "extremist literature." Kasparov said the raid was an apparent attempt to disrupt the planned protests.
"There are reasons to believe the move is linked to the opposition march scheduled for December 16," he told reporters.
Some 8,500 security personnel will be on duty to maintain law and order in central Moscow during the weekend's demonstrations.
