When a corporation's actions with its own private property becomes a threat to the public good, it is well within the purview and established precedent of government to regulate that specific corporation.
They didn't selectively choose this media organization, they did it for every single page. Users still have choice to see the content, if they are interested. I would argue that engagement should be higher if people actively opt in to view this content, as opposed to having it mixed in with their social feed.