The EC decided to send Hungary a "reasoned opinion" on the matter, the second and penultimate step in an infringement procedure.

The commission said it considers the measure, which allows authorities to block exports of building materials, to "have an equivalent effect to a quantitative restriction on exports within the internal market", and to be in breach of the Single Market Transparency Directive, which requires member states to notify the Commission about technical regulations and refrain from their adoption during a standstill period.

The measure, which also applies to Hungary's exports to countries outside of the EU, "appears to exceed Hungary's competencies under the common commercial policy, which is an area of Union exclusive competence", it added.

Hungary launched the measure last summer to curb runaway building materials prices.