The new tax, applicable from 1 April 2013, ranges from 3 euros to 7.50 euros a day depending on the size of the car. Even if you've paid upfront for the car hire you will still need to pay for this at the rental desk.
According to the Sunday Times, "Mallorca, Minorca and Ibiza are already the most expensive car rental locations in Spain, with peak-season rates up to twice that charged on the mainland."
The Balearic Islands government says the new tax will raise £13m to be spent on social and green projects.
By the way, we've done some reseaerch on the costs of excess insurance over the Easter period and found that in some locations unsuspecting travellers could be charged by the rental company up to £168 for a week's car hire excess insurance - this is over eight times the cost of an iCarhireinsurance.com policy at £21 for the (at £2.99 a day).