London (CNN Business) Germany's carmakers have been accused by the European Union of collusion in holding back technology to reduce harmful emissions from vehicles.

The European Commission said Friday that Volkswagen, BMW and Daimler broke antitrust rules by acting together to delay the introduction of two emissions cleaning systems between 2006 and 2014.

Margrethe Vestager, the bloc's top competition official, said in a statement that companies can cooperate to improve their products, but they cannot agree not to compete on quality.

"We are concerned that this is what happened in this case," she said. "As a result, European consumers may have been denied the opportunity to buy cars with the best available technology."

Regulators accused the carmakers of colluding at their annual "circle of five" technical meetings, which are attended by BMW, Daimler, Volkswagen and its subsidiary brands Audi and Porsche.

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