The European Commission on Monday implored national capitals to act with restraint in imposing new border controls after several EU members, including Germany, unilaterally ordered an array of restrictions in a frantic bid to slow the coronavirus pandemic.

The border measures threaten to undermine the EU's four fundamental freedoms — the movement of goods, services, capital and people — and to seriously destabilize the bloc's treasured single market, as well as to render meaningless the Schengen border-free travel zone.

The new internal checks also show how the coronavirus crisis has also called into question other benefits of EU membership for the union's 440 million citizens, such as the blue European health cards that entitle residents of any EU country to access health care anywhere else in the bloc — including in the U.K., which is still in a transition period following Brexit.

Separately, the EU is planning to impose a 30-day ban on "non-essential travel" into the Schengen zone from outside countries. Commission President Ursula von der Leyen and Council President Charles Michel said at a news conference that they had informed other G7 leaders of their plans during a conference call. "We will have to take measures to limit and slow down the spread of the virus," von der Leyen said.

The border measures taken by national capitals have prompted speculation that some governments are acting not so much to stop the spread of the virus, but to block citizens of other EU countries from crossing boundaries to access doctors and hospitals — a potentially severe test of EU solidarity.

The guidelines on border measures came as the EU and national governments wrestled with a crisis unlike any other in modern times.

In a four-and-a-half page set of guidelines published on Monday, the Commission effectively conceded defeat in any effort to prevent new internal border controls.

Instead, Brussels sought to persuade EU capitals to act judiciously by not imposing measures that would hamper the single market — particularly the shipment of vital medical supplies — and by not denying medical care to EU citizens who might appear at border crossings showing signs of illness.

The Commission also tried to persuade capitals that border restrictions would not necessarily help contain the virus given that it has now spread to every EU country.

"The assessment that we have is that the virus is, at the moment that we speak, already present in all European member states, and therefore that closing borders is not necessarily the best way of ensuring that we can contain further the outbreak within the European Union," the Commission's chief spokesman, Eric Mamer, said at the EU executive's daily news conference. "At the same time, we recognize that member states have been acting in accordance with the information that they have," he said, in a bid to protect their own citizens.

Mamer conceded that member countries had not acted entirely in keeping with the Commission's wishes, and other officials said Brussels did not yet have a full grasp of the different border measures imposed by capitals — though legally EU countries are supposed to inform the Commission before taking any such steps.

"We are in a very fluid context, and what we have been saying is that these measures in order to be effective need to be very well coordinated and implemented," Mamer said. "But we have also been saying that governments have a responsibility to protect the health of their citizens."

The guidelines on border measures came as the EU and national governments wrestled with a crisis unlike any other in modern times, with citizens frightened over the possibility of infection, health care systems at risk of being overwhelmed, and widespread containment measures that have paralyzed commercial activity, with the full economic shock still to come.

The EU's commissioner for the internal market, Thierry Breton, said Monday that he expected a recession to take hold in the EU this year. Commission officials said they had not formally updated their forecasts but that Breton's prediction was likely correct.

The European Council scheduled another emergency summit by videoconference of EU heads of state and government for Tuesday afternoon. And leaders of the G7 economic powerhouses were scheduled to hold a conference call Monday afternoon amid growing signs of tension, including reports that U.S. President Donald Trump sought to buy a German company working to develop a vaccine for COVID-19.

The Commission noted that EU countries could carry out health checks and restrictive measures on those infected with coronavirus without imposing new border control regimes.

On the border issue, while the Commission tried to avoid a direct conflict with the national governments, its new guidelines made clear just how problematic it finds some of the new restrictions.

"In order to avoid shortages and avoid that the social and economic difficulties that all European countries are already experiencing worsen, maintaining the functioning of the Single Market is key," the Commission wrote in the guidelines, which are not legally enforceable. "Member States should therefore not undertake measures that jeopardize the integrity of the Single Market for goods, in particular of supply chains, or engage in any unfair practices."

The guidelines sought to remind capitals that they "must always admit their own citizens and residents and facilitate transit of other EU citizens and residents that are returning home."

And it also reiterated the rules for imposing such restrictions, even as capitals appeared to be ignoring those requirements, including that any restrictions on the transport of goods and people on the grounds of public health be transparent and have clearly spelled out reasons justified by medical experts, that they be proportionate; non-discriminatory; and timely.

"Member States should preserve the free circulation of all goods," the Commission urged. "In particular, they should guarantee the supply chain of essential products such as medicines, medical equipment, essential and perishable food products and livestock."

The Commission noted that EU countries could carry out health checks and restrictive measures on those infected with coronavirus without imposing new border control regimes.

In the guidelines, the Commission urged new entry screening measures, to assess the presence of symptoms or exposure to the virus, as well as exit screening measures. "Travelers identified as exposed to, or infected with Covid-19 should not be allowed to travel," the Commission wrote, adding those who are sick should be transferred to a health care facility.

"The authorities on both sides of the border should agree on the appropriate handling of cases of people considered as posing a public health risk such as further tests, isolation or quarantine and health care — either in the country of arrival or by agreement in the country of departure," the Commission wrote.

While the Commission did not directly rebuke member countries, some legislators were openly outraged by governments' moves to put up borders.

“I am most concerned that we are again sending a very discouraging message to the European citizens now,” said Juan Fernando López Aguilar, chair of the European Parliament’s Committee on Civil Liberties, Justice and Home Affairs.

Speaking to POLITICO by phone from Spain, the Socialist MEP said that “we are seeing measures taken unilaterally by member states with no coordination, with no horizontal information, with no calculation of the consequences … and with no consistency with European law, which provides procedures and conditions in order to adopt exceptional decisions.”

Extraordinary measures under the Schengen Borders Code “cannot be unilateral and of course they cannot be discriminatory against European citizens,” he added.

Jacopo Barigazzi, Lili Bayer and Rym Momtaz contributed reporting

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