Updated

A massive air traffic controller sickout Friday on the eve of a long holiday weekend caused travel chaos throughout Spain, forcing authorities to close eight airports, including the major European hub in Madrid.

The controllers left their posts amid a lengthy dispute over working conditions and just hours after the administration of Prime Minister Jose Luis Rodrigo Zapatero approved an austerity measure to partially privatize airports, and to hand over management of Madrid and Barcelona airports to the private sector.

Spain's air traffic authority, known as Aena, issued an advisory telling all passengers planning to take flights to stay away from airports because "air traffic has been interrupted" and there was no immediate word when the sickout might end.

Spanish media reported that a few international flights were landing at the Madrid airport, but that some passengers waited for hours in planes ready for takeoff before the planes returned to gates so the passengers could disembark.

Thousands of people were camped out in Madrid's airport Friday night, not knowing whether their flights would leave or not. Iberia, Spain's flagship carrier, said the Madrid airport could remain closed until 1 a.m. Saturday and that it was preparing a plan to move out delayed flights before dawn if the controllers start working again.

"All flights are blocked, there's a huge lot of people here, sitting around everywhere. Right now everyone is calm, but we don't know what's happening," stuck traveler Lola Molina told Spanish National Television.

Spain's air traffic controllers have been involved in a long negotiation process with state-owned Aena over wages, working conditions and privileges.

The dispute intensified in February when the government restricted overtime and thus cut average pay of controllers from €350,000 ($463,610) a year to around €200,000 ($264,920).

The sickout also closed four airports in the Canary islands and airports in the prime tourism destinations of Ibiza, Palma de Mallorca and Menorca.

In respons, Spanish Development Minister Jose Blanco convened an emergency meeting and his ministry issued a terse statement, saying "controllers have begun to communicate their incapacity to continue offering their services, abandoning their places of work."

The controllers' union has been complaining for weeks that members have already worked their maximum hours for all of 2010, and that the country's 2,000 controllers are overworked and understaffed. Friday's sickout was not expected, but the union has warned it could mount a sickout over the Christmas holiday. They are prohibited by law from going on strike.

Madrid's Barajas airport had 1,300 flights scheduled for Friday, but it wasn't clear how many had taken off and landed before the sickout.

For all of Spain, more than 5,000 flights were scheduled for the nation and about 3,000 had taken off or landed before the sickout began in the late afternoon.

Monday and Wednesday are national holidays in Spain, and many Spaniards use the period to take a five-day weekend.

Aena calculated that around 4 million people had booked flights for this period.

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Alan Clendenning and Jorge Sainz contributed from Madrid.