Answer:
To my knowledge, there are not really any requirements to fight fake news, however I am sure that soon social media companies will be forced by the government to do so because of the amount of fake news seen during the 2016 election.
Many social media companies like Twitter are fighting the spread of fake news by removing tweets and posts that contain false information.
On an unrelated note:
Those that say that the removal of certain people's accounts on social media is an infringement of their freedom of speech, are wrong. If you actually read the terms of service you would know that they reserve the right to remove you from their platform for violating these terms. Also, they are not regulated by the government. Therefore they have the right to remove accounts or posts from their site.
Explanation:
