The policy has been attacked by regulators and lawmakers who say it could spread misinformation and cause voter suppression. Critics including Democratic presidential candidate Elizabeth Warren have also run intentionally false Facebook ads to highlight the issue.
Facebook's chief executive Mark Zuckerberg has defended the company's stance, arguing that it does not want to stifle political speech, but he also said the company was considering ways to refine the policy.
Facebook does fact-check content from political groups. The company also says it fact-checks politicians if they share previously debunked content and does not allow this content in ads.
Twitter Inc has banned political ads. In November, it said this will include ads that reference a political candidate, party, election or legislation, among other limits.
The company also said it will not allow ads that advocate for a specific outcome on political or social causes.
"We believe political message reach should be earned, not bought," said Twitter CEO Jack Dorsey in a statement last month.
Some lawmakers praised the ban but critics said Twitter's decision would benefit incumbent and hurt less well-known candidates.
Officials from the Trump campaign, which is out-spending its Democratic rivals on Facebook and Google ads, called the ban "dumb" but also said it would have little effect on the president's strategy.
The overall political ad spend for the 2018 U.S. midterm elections on Twitter was less than $3 million, Twitter’s Chief Financial Officer Ned Segal said.
"Twitter from an advertising perspective is not a player at all. Facebook and Google are the giants in political ads," said Steve Passwaiter, vice president of the Campaign Media Analysis Group at Kantar Media.
Google said on Wednesday that it would limit audience targeting for election ads to age, gender and general location at a postal code level.
The change means political advertisers can no longer target ads using data such as public voter records and general political affiliations such as right-leaning, left-leaning or independent. Advertisers can still do contextual targeting, such as showing ads to users watching a certain video.
Google and its video-streaming service YouTube prohibit certain kinds of misrepresentation in ads, such as misinformation about public voting procedures, political candidate eligibility based on age or birthplace or incorrect claims that a public figure has died.
Google does not have a wholesale ban on politicians running false or misleading ads. In October, when former Vice President Joe Biden's campaign asked the company to take down a Trump campaign ad that it said contained false claims, a Google spokeswoman told Reuters it did not violate the site's policies.
Snap Inc allows political advertising unless the ads are misleading, deceptive or violate the terms of service on its disappearing message app Snapchat.
The company, which recently joined Facebook, Twitter and Google in launching a public database of its political ads, defines political ads as including election-related, advocacy and issue ads.
Snap does not ban "attack" ads in general, but its policy does prohibit attacks relating to a candidate's personal life.
The Chinese-owned video app popular with U.S. teenagers does not permit political advertising on the platform.
In an October blog post, TikTok said that the company wants to make sure the platform continues to feel "light-hearted and irreverent."
"The nature of paid political ads is not something we believe fits the TikTok platform experience," wrote Blake Chandlee, TikTok’s vice president of global business solutions.
The app, owned by Beijing-based tech giant ByteDance, has recently come under scrutiny from U.S. lawmakers concerned the company may be censoring politically sensitive content, and raising questions about how it stores personal data.