The decision was the last step in a process that protects traditional carriers such as Air France-KLM but has angered airports and budget airlines such as Britain's easyJet.
Current rules force airlines to use the time slots at busy airports at least 80 percent of the time or face losing them the following season, but some big airlines argue this obliges them to keep flying even when it is uneconomical.
"Having to permanently give up a slot is an extreme option which the airlines will avoid if they can," said Ulrich Schulte-Strathaus, secretary general of the Association of European Airlines (AEA).
"But flying nearly empty to protect slots is neither economically nor environmentally responsible," he added.
Air carriers will be entitled to the same series of slots during the summer 2010 season as were allocated in 2009, regardless of how much they use them, the European Parliament agreed, with 508 votes for and 20 against.
Airlines have been hit hard by the global economic slowdown, with some forecasting a 5 percent dip in traffic in 2009.
"Right now, we cannot predict how long this current downturn will continue," said the AEA's Schulte-Strathaus. "We have nothing to benchmark it against - it has already exceeded in severity any past economic upheavals in our industry."
Budget airlines say the proposed freeze will prevent the proper functioning of a market precisely when it should punish high-cost carriers.
"This a measure designed purely to help some ailing dinosaur airlines," said an easyJet spokesman. "There are other airlines waiting to take their place. It is discrimination against efficient airlines like easyJet and counterproductive to the aim of easing the recession."
Airport body ACI Europe said the move would hurt airports by constraining revenues in the midst of the crisis.
"Unlike airlines which have the flexibility to ground aircraft or cut routes and capacity at short notice to save costs, airports are bound by significant long term financial commitments linked to the development of their infrastructure," said ACI director general Olivier Jankovec.
(Reuters)
