X has blocked the European Commission from making adverts on its platform - a move which comes a few days after it fined Elon Musk's site €120m (£105m) over its blue tick badges.
Nikita Bier, who has a senior role at the social media site, accused the European Union (EU) regulator of trying to "take advantage" of "an exploit" in its advertising system to promote its post about the fine on Friday.
"It seems you believe that the rules should not apply to your account," he said. "Your ad account has been terminated."
A European Commission spokesperson told BBC News the Commission "always uses all social media platforms in good faith".
X's fine, issued on Friday, was the first under the EU's Digital Services Act.
