The European Commission, which announced Thursday an inquiry into Microsoft's promotion of its Teams messaging app, has fought US tech giants on fronts from tax avoidance, disinformation and hate speech to data privacy and monopolistic practices.
Here is a summary of the tussles between Silicon Valley and Brussels.
The European Commission on Thursday said it would investigate whether Microsoft was "abusing and defending its market position" by bundling its Teams app with its Office suite.
It comes a month after the commission recommended that Google sell off part of its business following a two-year probe into its dominance of online advertising.
If Google fails to comply it could face a fine of up to 10 percent of its global revenue under the 2022 Digital Markets Act.
Brussels has already slapped over eight billion euros in fines on Google for abusing its dominant market position.
In 2018, the company was fined 4.3 billion euros ($4.8 billion) -- the biggest ever antitrust penalty imposed by the EU -- for abusing the dominant position of its Android mobile operating system to promote its search engine.
The fine was later reduced to 4.1 billion euros.
The firm has also incurred billion-plus fines for abusing its power in the online shopping and advertising sectors.
Apple has also been in the EU's sights, with Brussels investigating its dominance among music streaming apps.
The EU has had less success in getting tech companies to pay more taxes in Europe, where they are accused of funnelling profits into low-tax economies like Ireland and Luxembourg.
In one of the most notorious cases, the European Commission in 2016 found that Ireland granted illegal tax benefits to Apple and ordered the company to pay 13 billion euros in back
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