A preliminary probe in this connection started in 2019 and the current investigation will examine if Google has been distorting competition by restricting access to user data while reserving such data for its own use, the European Commission said on Tuesday, CNN reported.

"Google collects data to be used for targeted advertising purposes, it sells advertising space and also acts as an online advertising intermediary. So Google is present at almost all levels of the supply chain for online display advertising," EU chief antitrust official Margrethe Vestager said in a statement.

"We are concerned that Google has made it harder for rival online advertising services to compete in the so-called ad tech stack."

A Google spokesperson said the company would cooperate constructively with European Commission "to answer their questions and demonstrate the benefits of our products to European businesses and consumers," according to a CNN report.

Google is already being investigated in a a number of antitrust cases in the United States. The United States government has also accused Google in one of the cases of operating an illegal monopoly for online search and search advertising, the CNN report stated.

The European Union spending on total display advertising 20 billion Euros or $24 billion in 2019. This business is mainly dominated by Facebook and Google, the report informed.

Facebook is already undergoing investigations on charges that its treatment of data allows it unfair advantage, said the report.

The EU authorities have accused Google of giving preferential treatment to Google Ad manager by favouring its own online ad marketplace AdX where publishers sell space to advertisers in real time, according to the CNN report.

In France, Google has agreed to make it easier for publishers to use its data and tools with other ad technologies.

The European Union watchdog will focus on a number of areas of concern including if it is obligatory to use Google services to purchase or serve ads on Google or YouTube, the CNN report stated.

This is because Google provides a number of services that are intermediate between the publishers and ad providers for advertising on mobile apps and websites.

Google earns about 80 per cent of its revenue from advertising, the CNN report informed.

It has stressed that competition in online advertising has opened more options for advertisers, reduced ad tech fees and made it more affordable.