Judge Marina Syrova is expected to issue a ruling Friday in the trial of Nadezhda Tolokonnikova, 22, Maria Alyokhina, 24, and Yekaterina Samutsevich, 30 -- members of the protest band Pussy Riot who were arrested in March after the band posted online video of a performance in Moscow's Cathedral of Christ the Savior.
Authorities who announced the extra security for the judge did not specify what, if any, threats had been made, The New York Times reported.
Worshipers appear divided over the potential fate of the band members for their protest.
If convicted, the women could face up to three years in jail.
A poll conducted in late July by an independent pollster found 58 percent of 1,600 people asked said a jail term for the trio would be excessive, while 33 percent said the women should go to jail.
Russian President Vladimir Putin -- the target of the band's protest -- said during the Olympics Pussy Riot had not done "anything good" but should not be judged severely, the Times reported.