Twitter is banning all ads that mention specific candidates, elections, or legislation. The ban on any advertising applies to campaigns, government officials, PACs and 501(c)(4) groups — that is, nonprofits designated for tax purposes as somehow promoting social welfare, a broad category covering groups spanning from the Sierra Club to Koch-backed Americans for Prosperity.

The total ban on political ads, however, does not extend to so-called issue ads — "cause-based" advertising in Twitter parlance — addressing topics like "economic stewardship" or "economic growth," according to a fact sheet the company supplied to press. While those issue ads will be allowed from any advertisers not otherwise prohibited from buying ads, there are significant new restrictions on their messaging and reach.

“We very much believe that cause-based advertising has value and can help drive conversation around important topics," said Del Harvey, Twitter's vice president of trust and safety, but "we're really trying to ensure there isn't an attempt to game our political content policy through cause-based advertising."

Under the new policy, those ads can't call for political or regulatory outcomes, and anyone placing them won't be able to target them at users with the same pinpoint accuracy afforded to other types of advertising. Issue advertisers won't be able to drill down to narrow geographies — in the case of the U.S., that means they can't geographically target ads more narrowly than the state level — and they won't be allowed to target users by political keywords that come up in their data-driven Twitter marketing profiles, such as "liberal" or conservative."

For-profit organizations running issue ads must not call for particular political outcomes, and such ads must reflect the organizations' “publicly stated values, principles, and/or beliefs," Twitter said.

Under the new rules, news publishers will be granted an exemption to run ads on political topics, as long as they don't advocate for a particular political outcome.

CEO Jack Dorsey had previewed the policy last month in a series of tweets that seemed aimed squarely at marking a stark departure from Facebook's approach. Many conservatives and some liberals at the time criticized the company's move.

“This is entirely new terrain," said Gadde. "We’re going to have to build out a lot more detail, especially globally."

The policy is set to go into effect Nov. 22.