The EU's powerful anti-trust regulator slapped tech giant Google with a new fine on Wednesday over unfair competition, in Europe's latest salvo against Silicon Valley.

"Today the commission has fined Google 1.49 billion euros ($1.69 billion) for illegal misuse of its dominant position in the market for the brokering of online search adverts," EU Competition Commissioner Margrethe Vestager said.

In its third major decision against the search engine behemoth, Brussels sanctioned Google's AdSense advertising service, saying it illegally restricted client websites from displaying ads from ad service rivals.

The original complainant in the decade long case was Microsoft, but the US software giant later pulled out of the case.

The fine brings Google's total tab with the EU to 8.2 billion euros in less than two years.

In July 2018, the US giant was ordered to pay a record 4.34 billion euros for abusing the dominant position of Android, its smartphone operating system, to help assure the supremacy of its search engine.

A year earlier it slapped Google with a fine of 2.42 billion euros for abusing its dominant position by favouring its "Google Shopping" price comparison service in search results.

Google has appealed both decisions to the European Court of Justice in Luxembourg.