Twitter’s plan to ban all political advertising risked muzzling climate activists while giving polluters free rein to promote themselves, the US presidential candidate Elizabeth Warren said.

“Twitter’s new ad policy will allow fossil fuel companies to buy ads defending themselves and spreading misleading info but won’t allow organisations fighting the climate crisis to buy ads holding those companies accountable,” she tweeted, linking to an environmental newsletter.

The announcement by Twitter was generally well received by critics of the state of online political advertising.

The company’s chief executive, Jack Dorsey, had taken a sideswipe at Facebook, tweeting: “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’.”

But a follow-up from Twitter’s general counsel, Vijaya Gadde, revealed that the company was considering extending the ban beyond political advertising to “issue ads”. Gadde said the company was considering outlawing “ads that advocate for or against legislative issues of national importance (such as climate change, healthcare, immigration, national security and taxes)”.

The mention of climate change stoked concerns that the rules could allow oil companies to promote the benefits of fossil fuels while barring critics from noting the related carbon dioxide emissions and the contribution to the climate crisis.

Dorsey responded to Warren’s criticism by saying that the new rules were not yet in place and would not be revealed publicly until 15 November – 10 days after elections in the US and a little under a month before the UK general election.

Adam Mosseri, the head of Instagram, backed Warren, saying: “[Her point] is one of the key issues many miss about banning political ads on any platform. You can’t ban these ads without significantly inhibiting the ability of activists, labour groups and organisers to make their cases too.”

Since he was promoted last year, Mosseri, who had been Instagram’s vice-president of product, has become one of the public faces of Facebook (Instagram’s owner), actively wading into policy debates on Twitter in a way Mark Zuckerberg, the chief executive, and Sheryl Sandberg, the chief operating officer, do not.