The mayor of Madrid says she will appeal to Spain's constitutional court against the country's new energy-saving regulations.
Isabel Diaz Ayuso said "the decree goes against trade, tourism and the feeling of security."
Despite the opposition's arguments, the controversial new energy policy will come into force as planned on August 10.
The measures require businesses to restrict air conditioning to no cooler than 27C in summer - and limit heating to below 19 degrees in winter.
The measure applies to airports, bars, cinemas, rail stations, shopping centers, theaters and hotels - although ministers say there is leeway for restaurant kitchens, gyms, and nightclubs.
The government also wants shops to make sure that store fronts go dark from 10pm local time.
The mayor of Madrid is up for the fight. /Susana Vera/Reuters
Ministers say the 17 regional authorities in Spain will have to "apply and monitor" the rules, though any decision on penalties for non-compliance will be left to each region's authorities to decide.
The measure will have a widespread impact - affecting stores up and down the country, which have had to ensure they get ready for the changes.
"We already have our air conditioning set above 25C and we make sure our door is always closed," said Ignacio Garcia, the manager of a watchmaker in the central Madrid.
"We also have outside lights that will have to be turned off to comply with the new law."
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EU nations trying to save energy ahead of 'difficult' winter
Spain is trying to reduce its energy use by 7percent ahead of what the European Union predicts could be a difficult winter for energy supplies, due to Russia's conflict with Ukraine.
The EU says it has tried to be as united as possible in its plan to wean itself off a reliance on Russian gas.
Spain itself does not depend on Russia for its energy as much as other European Union nations - but it has agreed to cut gas use by 7 percent.
The majority of the gas that Spain uses comes either from cargo deliveries from the United States, or via undersea pipelines from Algeria.
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