Oh what a tangled web we weave. This thing is not only unfair, it's a mess. The EU has created a rod for its own back that it is determined to proceed with at all costs, though with the price of carbon dropping through the floor they now have to engineer ways to make sure that they don't end up collecting the square root of FA.
And if the ICAO explicitly confirms that such a taxation is not conform with its statutes the EU will have to comply or unsign the ICAO statues.
The problem with this is that the EU, being a bunch of unelected eurocratic eejits, have no rights whatsoever in ICAO - they are merely observers. Only nation states have rights in UN organisations like ICAO. The EU mechanism is a bit difficult - the EU produces a directive. When that is done, each member state is obliged to enshrine the directive in their national law. So the problem is that nobody can actually take action against the EU itself in any way other than what the Chinese are actually doing, which is effectively direct action - trade war - and that the US has tried to do (through the ECJ - who may be a tad biased). But the EU numpties can't see this and we must all self-flagellate over our CO2 emissions sins.
Add to this that there's supposed to be a credit for flying with biofuel (what's the credit? Proportional to what is actually used? How do you prove what you actually used? How do you prove what % biofuel you actually have in your tanks at any one time); that carriers from other countries taking 'equivalent measures' may be exempted but nobody can define what an equivalent measure actually is; and that there is currently no mechanism for handling a 'new entrant' in the first trading period; and it's easy to see that this is not only stupid legislation but also very badly thought out.
ICAO needs to put it's dentures back in. When it has some teeth again maybe this idiocy can be controlled, if not stopped.