Donald Trump ordered a wide-ranging review of the law that underpins how social media platforms operate, in a move which threatens to undermine legal protections internet companies have enjoyed for decades.

The US president on Thursday signed an order instructing his officials to re-examine the 1996 law that granted social media companies immunity from being sued for content which appeared on their platforms, or for removing content. Section 230 of the law, the Communications Decency Act, has been dubbed the “26 words that created the internet”.

The president’s review — one of several moves designed to check what his supporters say is anticonservative bias shown by social media companies — comes after a bitter row with Twitter, which placed “fact check notices” against two of his tweets earlier this week.