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BRUSSELS (Reuters) - The EU executive on Thursday asked the bloc’s top court to take action against Spain and Bulgaria over their poor air quality, warning that the countries were failing to protect citizens against pollution.

Spain exceeded limits of nitrogen dioxide, specifically in the two big cities of Madrid and Barcelona, where the legal levels are constantly exceeded, the European Commission’s decision stated.

“The newest air quality data provided by Spain confirms the systematic breach of EU rules on nitrogen dioxide values, which have been legally binding since 2010,” the Commission said, referring the matter to the Court of Justice of the EU.

The decision could complicate an attempt by Madrid’s new conservative council to lift a low-emission scheme that permits only certain vehicles, primarily electric and hybrid cars, to enter the restricted central area. A judge last week blocked the council’s attempt to lift the restrictions.

Nitrogen dioxide causes about 9,000 premature deaths every year in Spain, according to the European Environment Agency.

In Bulgaria, data showed that the country was exceeding sulfur dioxide levels, its second instance of non-compliance with the bloc’s air quality standards. In 2017, the court ruled the country was not within the limits for particulate matter.

The Commission did not say in its statement if it has asked the court to consider fines, but under the EU’s so-called infringement procedure, financial penalties of either a daily payment or a lump sum can eventually be imposed.

The Commission also said on Thursday it had sent a letter to Poland warning of legal action for failing to comply with a 2018 air quality decision, notably in transport and the replacement of what it said were outdated solid fuel boilers used for heating households.

The EU executive also urged Croatia and Romania to address failures in monitoring pollution.