According to this Fortune article, The European Commission is making steps towards "normalizing" taxation for tech companies:
The European Commission wants to see big tech firms pay a 3% tax on some of their revenues. This is a major break from the traditional way of calculating tax based on profits.
The European Union’s executive body is frustrated with the relatively low corporate taxes paid by firms such as Facebook and Amazon, and individual EU countries are frustrated at seeing overseas firms take business from local rivals while booking their revenues elsewhere.
In the long term, the Commission wants to see the EU’s corporate tax rules reformed so that companies are taxed on their profits based on the location of their customers and users, rather than the location of their headquarters
One example of very low taxation is represented by Amazon which managed to pay about 0.1% in taxes (£15m / £19.5bn).
On the other hand, trade lobbyists see this initiative as discriminatory:
“The proposed turnover tax aimed at online platforms is discriminatory and ignores the global consensus that the so-called ‘digital economy’ should not be singled out,”
From my POV, revenue taxation instead of profit based taxation seems to the only significant issue, since it might not take into account small profit margins (e.g. Retailers may have profit margins as small as 0.5%).
Question: Why does taxation of big tech companies seem so problematic? Why does having a similar (to companies having a physical presence) level of taxation for them seem so difficult to achieve?