Twitter has announced it is banning all political ads ahead of the 2020 US Presidential Election season, striking a sharp contrast from Facebook which is still defending the practice.

"While internet advertising is incredibly powerful and very effective for commercial advertisers, that power brings significant risks to politics, where it can be used to influence votes to affect the lives of millions," Twitter CEO Jack Dorsey said Wednesday in a series of posts.  "It's not credible for us to say: 'We're working hard to stop people from gaming our systems to spread misleading info, but if someone pays us to target and force people to see their political ad.. well.. they can say whatever they want!'" he continued.

Zuckerberg responded by he defended Facebook's decision to allow political ads even if they contain false information.

"Some people accuse us of allowing speech because they think all we care about is making money, and that’s wrong," Zuckerberg said, "I can assure you that from a business perspective, the controversy this creates far outweighs the very small percentage of our business that these political ads make up."

The Facebook boss has come under widespread criticism for the decision, which detractors say will allow all sorts of meddling in the upcoming US election.  Some of that heat is coming from his own employees.

A letter signed by 250 Facebook workers warns the absence of fact-checking in its political advertisements is "a threat to what FB stands for", and the company's policy "doesn't protect voices, but instead allows politicians to weaponize our platform by targeting people who believe that content posted by political figures is trustworthy," the letter reads.

"We strongly object to this policy as it stands," the workers wrote.