"I am convinced that such a move does not correspond with the spirit of the new relations established between Russia and NATO, and fails to answer modern security concerns," said Lyubov Sliska, who also serves as a deputy speaker in the State Duma lower house of parliament.
Her comments came during a meeting in Moscow of the Russia-NATO parliamentary assembly, which was devoted to security and economic affairs.
Sliska, who is a close ally of President Vladimir Putin, said Moscow was especially concerned about the well-being of ethnic Russians who live in the Baltics, and possible discrimination against them following NATO's expansion.
"I would like to express particular concern about the state of ethnic minorities living in Latvia and Estonia," she said.
"Hundreds of thousands (of Russians) still do not have citizenship" in those countries, she noted.
Sliska added that Russia's relations with NATO would be complicated further should problems concerning ethnic Russians in the Baltics remain unresolved following the bloc's eastward expansion.
The three Baltic states are in a group of seven former Communist bloc nations that have received invitations to join the alliance, and are expected to formally join the bloc next May.
Putin and other top Russian officials have fought the expansion, although the Russian leader has recently toned down his criticism of the plan.