https://techcrunch.com/2019/04/10/for-true-transparency-around-political-advertising-u-s-tech-companies-must-collaborate/

In October 2017 online giants Twitter, Facebook, and Google announced plans to voluntarily increase transparency for political advertising on their platforms. The three plans to tackle disinformation had roughly the same structure: funder disclaimers on political ads, stricter verification measures to prevent foreign entities from posting such ads, and varying formats of ad archives.

All three announcements came just before representatives from the companies were due to testify before Congress about Russian interference in the 2016 election and reflected fears of forthcoming regulation, as well as concessions to consumer pressure.