Essentially countries are forming a cartel to set bottom income tax. Forming cartels by private companies to „fix” prices is illegal, but countries are free to do it.

However, the actual mechanics of that tax is hard:

1. Countries can still do subsidies, but avoid touching income tax.

2. Taxing by income where revenue is generated is hard to compute. It would make sense to enforce it only on big multinationals. E.g. Big tech pay income taxes proportional to revenue from different countrues or/and where they employees are located.

3. Looking at statistics the ideal income tax floor should be around 19%.