The government has introduced gas rationing in an effort to mitigate the impact, ordering truckers to maintain regular gas supply to airports and emergency services.
Public transport has to be supplied by 75 per cent and gas stations by at least 50 per cent. Strikers said the requirements were illegal and vowed to ignore them, according to El Mundo daily.
Lines have been seen both in Portugal and across the border in Spain, with the worst shortages reported in the Atlantic region of Algarve, popular with tourists in summer.
Portuguese Prime Minister Antonio Costa has announced an energy emergency until next Wednesday as the government is struggling to avoid a second fuel crisis since April.