A tourist tax of five euros per day ($6.30) is part of the 2007 proposed budget in Italy. According to the BBC, there's some flexibility as to where and how the tax is applied. For instance, certain cities may not adopt it, and accommodation types such as youth hostels might be exempt.
Foreign tourists aren't being singled out here; vacationing Italians will have to pay the tax as well. It seems like cities such as Venice, which is coping with the fallout of climate change and hundreds of years of tourism, could really benefit from extra revenue to fund sustainability efforts.