"We believe people should know if the news they read is coming from a publication that may be under the influence of a government," said Facebook cyber policy executive Nathaniel Gleicher.
As Washington urges Russia's state-funded network to register as a "foreign agent," Moscow is considering restrictions on all international press.
Twitter cited U.S. intelligence community information in its decision to shut down RT and Sputnik's ads immediately.
Washington has requested the state-run network register under the Foreign Agent Registration Act over Kremlin links.
The Russian president also seemed to take a swipe at the BBC, CNN and other Western broadcasters.
Heads of government met today to draw up plans to counter Russia's "disinformation campaigns".
As reader-supported news vanishes, corporate-journalist hybrids may start drawing more red lines.