State-run channels repeatedly swung their cameras on to Dmitry Medvedev, favoured by President Vladimir Putin to succeed him in a March 2 election, when he attended an Orthodox Christmas Eve service in Moscow, they said.
"State television committed blasphemy by turning the transmission of the Christmas liturgy from the Church of Christ the Saviour into a show called 'the Birth of the successor'," senior Communist lawmaker Valery Rashkin said in a statement.
Cameras broadcasting the Jan. 6 service for the Channel One and Rossiya channels -- main source of news for most Russians -- focused on 42-year-old Medvedev instead of the altar, he said.
"All the thoughts of believers, and of any cultured person, at this moment are focused on one thing: the Saviour coming into the world. A church is not the place where the authorities and state television should organise reality shows," said Rashkin.
The service was led by Patriach Alexiy II. No one was available to comment on the broadcasts at either of the two television stations.
During last year's televised Easter service, Putin and senior Kremlin figures were shown on the altar when the Patriarch praised them for restoring Russia's stability.
Putin is required by the constitution to step down when his second term ends this year year. Opinion polls show Medvedev is overwhelming favourite to win the election because of endorsement from the popular Putin.
The opposition accuses the Kremlin of using its control of the biggest television stations to ensure positive coverage for Medvedev while giving his challengers only limited access to the airwaves.
After decades of state atheism under Communist rule, the Russian Orthodox Church is experiencing a revival. Politicians are frequently seen attending church services and the Communists -- now in opposition -- no longer espouse atheism publicly as they did during the Soviet era.
Many Orthodox churches celebrate Christmas on Jan. 7, not Dec. 25 as elswhere in the Christian world, because they operate on the older Julian calendar.