Reporters Without Borders said in a written statement that Romanova, a main anchor on the network, specialized in reports critical of the authorities, in particular the Kremlin's policy toward Russia's broadcast sector.
The group described Romanova's case as "particularly worrying" and said it was concerned about the future of REN-TV. It called the privately owned station the last bastion of independent broadcast media in Russia.
Romanova was told on 24 November that she could not broadcast that night. Security guards prevented her from entering the studio. The incident happened hours after Romanova told the Ekho Moskvy radio station that REN-TV's management was blocking her reports.
Romanova believes she was punished for disclosing an act of censorship at the channel. She has said she intends to take the case to the legal authorities.
"Olga Romanova's treatment is a clarion call that tells us that we have lost the last station that kept even a little independence and objectivity in its coverage," Interfax quoted former Soviet President Mikhail Gorbachev as saying.