Google was fined 1.49 billion euros (A$2.39 billion) on Wednesday for blocking rival online search advertisers, the third large European Union antitrust penalty for the Alphabet business in only two years.
The European Commission, which said the fine accounted for 1.29 percent of Google's turnover in 2018, said in a statement that the anti-competitive practices had lasted a decade.
"Google has cemented its dominance in online search adverts and shielded itself from competitive pressure by imposing anti-competitive contractual restrictions on third-party websites," European Competition Commissioner Margrethe Vestager said.
The case concerned websites, such as of newspaper or travel sites, with a search function that produces search results and search adverts. Google's AdSense for Search provided such search adverts.
The misconduct included stopping publishers from placing any search adverts from competitors on their search results pages, forcing them to reserve the most profitable space on their search results pages for Google's adverts and a requirement to seek written approval from Google before making changes to the way in which any rival adverts were displayed.
The AdSense advertising case was triggered by a complaint from Microsoft in 2010. Both companies subsequently dropped complaints against each other in 2016.
Last year, Vestager imposed a record 4.34 billion euro fine on Google for using its popular Android mobile operating system to block rivals. This followed a 2.42 billion euro fine in June 2017 for hindering rivals of shopping comparison websites.
Google is now trying to comply with the order to ensure a level playing field with proposals to boost price comparison rivals and prompt Android users to choose their preferred browsers and search apps. Critics however are still not happy.($1 = 0.8811 euros)
(Reporting by Foo Yun Chee; editing by Philip Blenkinsop and Alexander Smith)