LISBON (Reuters) - Portugal declared an “energy crisis” on Tuesday after a strike by fuel truck drivers hit the country, forcing the government to order striking workers to get back on the road immediately as airports resorted to emergency reserves.

FILE PHOTO: A plane takes off at Lisbon airport, Portugal July 5, 2018. REUTERS/Rafael Marchante/File Photo

Demanding better workers’ rights, fuel truck drivers started a strike on Monday but guaranteed the operation of minimum services. According to the Socialist government, however, the minimum service has not been provided and fuel supplies are running out.

In Faro, one of the country’s biggest tourist hubs, the airport resorted to emergency fuel reserves. Lisbon airport has also been affected.

“At both airports, where fuel supply wasn’t ensured, we have reached critical levels of fuel reserves for aircraft refueling,” Economy Minister Pedro Siza Vieira told reporters.

Alongside oil companies, Portugal’s government and security forces are sending dozens of tanker trucks to Lisbon to supply the capital’s airport with fuel.

An energy crisis was declared by the government on Tuesday evening, meaning security and emergency services now have priority when it comes to refueling at gas stations. In addition, an alert was issued to ensure security forces are mobilized to run fuel supply operations and guarantee people’s safety.

The government said in a statement the strike was also affecting fire stations, ports, public transport companies and gas stations.

“I want to ask drivers to comply with the law and with the determined minimum services required,” Siza Vieira said, explaining the decree passed ordering drivers to return to work.

The National Union of Dangerous Goods Drivers said the strike would continue until its demands are met.

Across the country, panicked drivers queued outside gas stations to fill up their tanks. More than 200 gas stations were already shut.

Only one flight has been canceled, but according to the minister, there could be more cancellations in the next few hours if supplies are not resumed.

Air traffic controllers said on Twitter that a Ryanair flight had to stop in Santiago de Compostela, in northern Spain, to refuel the aircraft before heading back to Lisbon.

Portugal’s national airline, TAP, has a contingency plan to reduce the impact of the strike.

Airport authority ANA is monitoring the situation and has asked passengers traveling from Lisbon or Faro to check their flight status with airlines.

Fuel company Prio, which operates in Portugal, told news agency Lusa that it expected almost half its stations to run out of gas or diesel by the end of the day.

“This could aggravate if the truckers’ union does not advise its members to comply with the order issued by the government to fulfill the minimum services to supply stations,” Prio said in a statement.

Portugal President Marcelo Rebelo de Sousa said the government was trying to “stabilize and normalize the situation”, especially with families traveling home for Easter.