The European Commission said Tuesday it has formally warned six EU countries that their virus-related border curbs could undermine free movement within the bloc.
Letters sent on Monday to Belgium, Denmark, Finland, Germany, Hungary and Sweden, highlight a risk of "fragmentation and disruptions to free movement and to supply chains," commission spokesman Christian Wigand told journalists.
The EU executive is worried the measures go beyond recommendations adopted four months ago seeking a "proportional" balance between slowing the spread of the coronavirus and maintaining movement.
It has given the countries until late next week to respond, failing which it could, theoretically, start proceedings for breach of EU laws.
Germany, however, strongly rejected the idea that its strict restrictions on traffic from Austria's Tyrol region and from the Czech Republic and Slovakia ran counter to EU rules.
"I reject the accusation that we have not complied with EU law," German European Affairs Minister Michael Roth said in Brussels, where he was attending a meeting of EU counterparts.
He said Germany had made the "difficult" decision because of the fear of highly contagious coronavirus variants and because of Germany's position as "a transit country in the middle of the European Union".
The commission's letter to Germany, obtained by AFP, said Germany was not applying all the ban exemptions set out by the EU recommendations, and noted that the spread of variants in the Czech Republic and Slovakia was no worse than in some other EU countries.
It also took exception to German authorities requiring Covid-19 test results to be issued in English, German, French or Italian, saying results in Czech or Slovak should also be accepted.
The EU's aim, the letter said, is "the preservation of the functioning of the Single Market during a volatile economic period, as well as the protection of family life during a time of significantly reduced social contacts outside the core family."
Wigand, the commission spokesman, said: ' We trust that we will find solutions with member states concerned without having to revert to legal steps, which can be lengthy".
EU leaders are to discuss the virus situation in the bloc on Thursday and Friday, during a videolink summit.