In a good year, tourism receipts add $2 trillion to the European economy, and so it was imperative for EU member states to devise a holiday-friendly action plan that could stand up to the worst of the COVID-19 outbreak. It involved opening internal EU borders and short-listing countries deemed to be COVID-safe; the U.S. did not make the cut.

Those measures first went into effect in mid-June, at the start of the busy summer travel season. But now a wave of coronavirus spikes and second-wave fears are forcing lawmakers to reassess the safety of European travel, putting the most sacred of European rituals—the lengthy summer vacation—in doubt.

Amsterdam was recently forced to close down its red-light district. “Corona and mass tourism just don’t go together—certainly not in a historic city center like in Amsterdam,” warned Mayor Femke Halsema. “There is a risk of contamination.”

That same risk is unnerving German lawmakers, who are now pushing for mandatory nasal swab tests for returning holidaymakers as the number of cases in Germany edges higher.

And the U.K. government over the weekend slapped sudden quarantine orders on those coming from Spain, creating havoc among travelers in both countries.

The U.K. measure was so sudden it caught Britain’s transportation secretary, Grant Shapps, completely off guard. He was in Spain when the decision came down. On holiday.

Transport Secretary Grant Shapps caught up in Spain rule change https://t.co/zJiF3C5aDg

— BBC News (UK) (@BBCNews) July 26, 2020

The U.K.’s move has infuriated the airlines—for British sun-seekers, Spain is a perennial favorite destination—and the Spanish authorities. On Monday morning, Spain’s foreign minister, Arancha González Laya, told reporters, “Spain is safe. It is safe for Spaniards. It is safe for tourists.”

Ryanair CEO Michael O’Leary sounded off too on Monday, calling the measure “a badly managed overreaction” on an earnings call with analysts and the press. Europe’s biggest budget airline can ill afford to lose more business this summer season. It’s already operating at 40% capacity across much of its network.

Wire photography:

Angel Garcia—Bloomberg/Getty Images

The quarantine orders contributed to what’s been a brutal day for Europe’s airline and travel sectors. Ryanair shares fell more than 4% at the open on Monday. Lufthansa and Europe’s biggest holiday company, TUI, saw even bigger share declines. That’s after TUI’s British unit warned it would cancel all holidays to mainland Spain through Aug. 9.

Investors and holidaymakers may not care for the abrupt restrictions and potentially dashed travel plans, but scientists are calling the moves sensible.

The quarantining of people returning from high-risk countries may seem like a “blunt tool,” says Adam Finn, professor of pediatrics at the University of Bristol, but it may prove an effective way to reduce the risk of importing the virus.

“The U.K. epidemic in March mostly came in the noses of U.K. nationals returning from France, Italy, and Spain—so once bitten, twice shy,” he says.