“We asked for a clarification, explanations from Danish authorities regarding this decision,” commission spokesperson Pia Ahrenkilde Hansen told AFP.
The EU’s executive arm, she said “will not accept any challenge to the principle of freedom of movement of goods and people in the European Union”.
Denmark vowed to follow rules under Europe’s passport-free Schengen travel area when it sends customs officers permanently at borders to conduct random checks on vehicles.
The new controls will enter into force within two to three weeks, Finance Minister Claus Hjort Frederiksen said following an agreement between the government and the far-right.
The Danish decision came a day before EU interior ministers hold a special meeting in Brussels to discuss the possibility of temporarily restoring border controls within the EU amid fears of a wave of north African migrants.
The European Commission proposed last week to introduce a mechanism that would allow states to temporarily reinstate checkpoints during sudden surges in migration or if an EU country fails to control its frontier with non-EU nations.