The Balearic government, as reported last week, has ruled out introducing a tax on hire cars. It said that a tax wouldn't have any effect in reducing the number of cars (the government has been expressing concerns about how many there are), and it now also says that at present the tax has not been "technically thought through".
However, some members of Més want such a tax and believe that it can be introduced via a modification to the tourism law. The government, though, is also aware of the fuss that was created when the Partido Popular administration of José Ramón Bauzá contemplated such a tax. The PP had intended bringing in three main types of "green tax", and this was one of them. In the end, none of them were pursued. In the case of a tax on large retail centres, the government faced a potentially fierce battle in the courts. It backed down.
Any tax on hire cars would be payable by the user, but the government would have a problem because it doesn't have a complete register of all the cars, many of which are shipped on to the islands by multinational companies.
If it were able to apply a hire-car tax, the government might not be going to increase the tourist tax next year (in some form or another). The level of government spending will rise in 2018, and so some additional revenue from specific taxes will be needed.