The European Union (EU) opened a formal antitrust investigation into allegations that Google abuses its leading role in the advertising-technology sector, the European Commission said in a statement on Tuesday.

The investigation comes as the EU is preparing new laws to better oversee tech giants by giving them special "gatekeeper" rules that would more tightly regulate how they can operate, but those will not be implemented for years. 

The case opens yet another front by the European Commission against the search engine giant, which has already received 8 billion euros ($9 billion) in fines for its anti-competitive practices. The Commission said it would investigate whether Google distorts competition by restricting third-party access to user data for advertising purposes on websites and apps while reserving such data for its own use.

"We are concerned that Google has made it harder for rival online advertising services to compete in the so-called ad tech stack," European Competition Commissioner Margrethe Vestager said in the statement.

Google generated $147 billion in revenue from online ads last year, more than any other company in the world, with ads including search, YouTube, and Gmail accounting for the bulk of its overall sales and profits.

About 16 percent of its revenue came from the company's display or network business, in which other media companies use Google technology to sell ads on their website and apps.

Reuters reported on Tuesday citing market researcher eMarketer that Google could control 27 percent of global online ad spending this year, including 57 percent for search ads and 10 percent of the display.

The company "will continue to engage constructively with the European Commission to answer their questions and demonstrate the benefits of our products to European businesses and consumers," a Google spokesperson said.

"Thousands of European businesses use our advertising products to reach new customers and fund their websites every single day. They choose them because they're competitive and effective," the spokesperson added. 

Google-owned technologies include services such as AdX, Doubleclick, or AdSense that power much of the EU's display advertising market for web pages and apps, which the commission estimated to be worth about 20 billion euros in 2019. 

Google's plan to remove browser cookies and also to stop tracking Android users via a tool known as an advertising identifier will also be looked at.

"We will also be looking at Google's policies on user tracking to make sure they are in line with fair competition," Vestager added.

(With input from Reuters and AFP)