The “centime sanitario” tax levied on petrol and diesel is against EU legislation, according to Nils Whal, chief lawyer to the EU.
The EU has taken the Spanish tax to the general court in Luxembourg which is expected to issue a ruling on the tax within the next few months. They are expected to rule against Spain, and order the return of around 13 billion euros collected via this tax.

Spain was taken to the courts after a complaint by a transport company against the tax in the courts of Barcelona. The Supreme Court there referred the matter to the EU, saying it was outside of its jurisdiction.
The idea behind the tax is that the different regions can levy it at different levels – it’s why fuel is cheaper in Murcia than Andalucía. The money is supposed to be used for green initiatives, and also supposed to act as an incentive for consumers to find an alternative to fuel.
The EU reckons it’s a stealth tax that runs against EU legislation and that the regions aren’t applying as they’re supposed to. If the court rules against Spain, all companies and people who have paid the tax can, in theory, ask for the tax back, although Spain has already asked for the courts to rule that they won’t have to return their ill gotten gains.