LISBON (Reuters) – Portugal’s government is set to ration fuel for the public and take special measures to ensure supplies to hospitals and airports in preparation for a planned strike by tanker drivers.

The government’s decision on Friday to declare an energy crisis indicates it expects negotiations between drivers and their employers to fail and that an open-ended strike will start on Monday.

Fuel rationing, which will restrict car drivers to a maximum of 15 litres of petrol or diesel at specially designated stations, will start at midnight Saturday and is scheduled to last until Aug. 21.

“The energy crisis aims to guarantee essential energy supplies for defence, functioning of the state and priority sectors of the economy,” the government said in a statement after the cabinet met.

A similar strike by fuel-tanker drivers in April caused low supplies at more than 2,000 petrol stations and prompted panic buying by drivers.

Drivers have again been rushing to filling stations, causing long queues in some cities, on fears that this strike could be worse as it comes at the height of the summer tourist season. A website providing information on the strike said 7% of the country’s filling stations were already running low.

The declaration of an energy crisis allows the government to ensure full supplies to ports, hospitals, airports, military bases, fire stations, the civil protection agency and some 320 key public petrol stations. It will also be able to mobilise the army to secure supplies.

The fuel tanker drivers are demanding higher wages and better working conditions. They will make a final decision on Saturday after last-minute talks with employers whether to go ahead with the strike.

Portugal is due to go to the polls in a national election in October when the ruling Socialists are on course to retain power.

(Reporting by Catarina Demony; Editing by Axel Bugge/Keith Weir)