NEW YORK (BLOOMBERG) - Facebook and Twitter tumbled the most in weeks after consumer giant Unilever said it would halt US ads on the social media platforms for the rest of 2020 because of concerns over hate speech and polarised American politics.

The move added the maker of Hellmann's mayonnaise and Axe shower gel to a growing list of high-profile consumer companies to pull ads from Facebook and Instagram.

Unilever's ban also sweeps in Twitter, which has also struggled to deal with offensive posts but has recently taken a more active stance than Facebook in some cases.

Facebook and Twitter both slumped to session lows on the news.

Facebook plunged as much as 8.6 per cent, the most intraday since March, while Twitter shares fell as much as 8.2 per cent.

"Our mission is to serve the public conversation and ensure Twitter is a place where people can make human connections, seek and receive authentic and credible information, and express themselves freely and safely," said Sarah Personette, Twitter's vice-president of global client solutions, in a statement.

"We are respectful of our partners' decisions and will continue to work and communicate closely with them during this time."

Facebook did not immediately respond to a request for comment on Unilever's decision, which was reported earlier by the Wall Street Journal.