YouTube and Instagram face being blocked by Russian internet service providers as a result of a standoff between one of the country's richest businessmen and an opposition leader.
Russia's internet censor blacklisted material on both services after a court ruled that it violated billionaire Oleg Deripaska's privacy rights.
A Thursday deadline has been set.
If neither Mr Navalny nor the US tech firms involved delete or otherwise block local access to the imagery by the end of the day, then Russia's ISPs will be required to take action themselves.
"It's impossible for internet providers to block certain pages on Instagram and YouTube," a spokeswoman for the Russian Association for Electronic Communications said.
Mr Navalny is Russia's most prominent opposition leader. But he has been barred from standing against President Putin in next month's election because of a corruption conviction, which he says is politically motivated.
Mr Navalny's Anti-corruption Foundation posted a video to YouTube last Thursday in which he presented footage that allegedly showed Mr Deripaska meeting Russia's Deputy Prime Minister Sergei Prikhodko aboard a yacht.
The material was said to have been sourced from a woman's Instagram account, where it had been posted in 2016.
Mr Navalny also uploaded a photo of the "secret meeting" alongside a post detailing corruption claims, to his own Instagram account.
Earlier, the government's internet watchdog Roskomnadzor issued the two tech platforms a take-down notice giving them three business days to comply.
Google subsequently wrote to Mr Navalny's team saying it might be forced to block the videos.