https://phys.org/news/2018-05-facebook-twitter-tighten-political-ads.html

Facebook said its new policy would be in effect as of Thursday for ads in the United States on Facebook and Instagram. It intends to implement the same policy worldwide in the coming months.

Twitter meanwhile said it would begin enforcing a new policy in the coming months that would require "election labels" for US candidate ads, and require notarized forms that verify the advertisers are in the United States.