Its relatively easy. All the big tech crops are paying effectively below 1% of their profits in Europe and are moving almost all of their profits to tax havens. As these companies are very creative when measuring their localized profits, its easier and more fair to impose a tax at the revenue level.

I don't understand all the negative comments here. Look at the big profit margins of all big tech companies (maybe with the exception of Amazon retail) and ask yourself whether a moderate, unavoidable tax is really unjustified or will have negative effects on anyone (except maybe the shareholders). I don't think so and in my opinion tech workers should be a bit more mindful when thinking about these taxation topics. I prefer paying high taxes strongly to further social segregation, which will lead to the development of civil unrest and lower quality of life for everyone sooner or later...

I was trying to avoid giving my opinion. My curiosity was specifically around what conditions make a company subject to this new tax and its purpose.

Aside from my opinion on corporate taxing and government approaches towards it in general, I will give an opinion on new taxation policy in general developed as a counter to avoidance. More and more frequently, legislation is drafted to combat the lack of enforcement of existing statutes. And that same legislation is similarly unenforced like its predecessors. Most watch this history repeat and cheer it on with incredulity towards disagreement. Some believe this time will be different, others believe the same institutions that are failing at their obligations shouldn't be given a mandate to fail using the same approaches. It adds more codified word and less substantive meaning. Replace tax structures (only if you must), enforce, move on. Don't pile on, leave unenforced, and keep giving pitchforks to the citizenry while ignoring the responsibility of the collectors.