US President Donald Trump has warned the European Union (EU) that it will "pay a very big price" for fining American tech companies.

"The European Union is at it again and, as usual, taking direct aim at GREAT American Companies!," Trump said in a post on Friday on Truth Social.

"The European Union will pay a very big price for this illegal and highly unethical conduct, which I have consistently warned them about." Trump made his post after the European Commission imposed a $1 billion fine on Alphabet Inc.’s Google (NASDAQ:GOOGL) on Thursday.

It ruled that Google had breached the bloc’s Digital Markets Act by favoring its own services in search results and restricting app developers from directing users elsewhere.

The penalty added renewed strain to US-EU relations at a moment when trade tensions between Washington and Brussels had appeared to ease.