The EU has warned Twitter boss Elon Musk that the social media company could face hefty fines if it fails to comply with the EU’s new digital rules.

Commenting on Musk’s plan for moderation and freedom of speech, Thierry Breton, the EU’s commissioner for the Internal Market, said Musk must follow rules to moderate illegal and harmful online content.

Breton’s remark came days after the EU signed the Digital Services Act, which will force the social media giants to take more aggressive measures to monitor content on their platforms.

If Musk fails to play by the rules, Twitter faces heavy fines and a possible ban.

“Anyone who wants to benefit from this market will have to fulfill our rules. The board [of Twitter] will have to make sure that if it operates in Europe it will have to fulfill its obligations, including moderation, open algorithms, freedom of speech, transparency in rules, obligations to comply with our own rules for hate speech, revenge porn [and] harassment. If [Twitter] does not comply with our law, there are sanctions—6 percent of the revenue and, if they continue, banned from operating in Europe,” Breton said.