The EU decision was blasted by civil liberties groups at the time, but the court did not rule on whether people's privacy was being invaded. In November, a top EU official rejected claims that the privacy of passengers had been violated.

The agreement between Brussels and Washington came as part of the security clampdown from the September 11, 2001, attacks in the United States.

Under it, airlines would be obliged to provide the US authorities with up to 39 pieces of data on passengers and crew -- including credit card information, addresses and telephone numbers -- 15 minutes before a flight's departure.

The appeal to the ECJ was brought by the European Parliament. The former president of the assembly, Pat Cox, said he believed that passengers' rights were being infringed by the transfers.

However the decision ruffled many feathers at the parliament because the assembly had been excluded from the process.

The Luxembourg-based top EU court gave the EU and the United States until September 30 to negotiate a new agreement. The data transfers can continue until then.

Gordon said the hunger strikers aimed to gain media attention to pressure the U.S. to release detainees held there as enemy combatants.

As many as 74 of the new hunger striking prisoners were refusing food but accepting liquids, while one had been required to be fed by a forced-feeding system, added Gordon, noting that the system was safe and humane.

The U.S. military currently holds some 500 detainees at Guantanamo, most of whom were captured in Afghanistan, with many having been held for nearly four years without charges.