Got European travel plans this summer? Don’t forget to pack your passport, sunscreen and plenty of patience.

After two years of pandemic restrictions, travel demand has roared back, but airlines and airports that slashed jobs during the depths of the COVID-19 crisis are struggling to keep up.

With the busy summer tourism season underway in Europe, passengers are encountering chaotic scenes at airports, including lengthy delays, canceled flights and headaches over lost luggage.

Schiphol, the Netherlands’ busiest airport, is trimming flights, saying there are thousands of airline seats per day above the capacity that security staff can handle. Dutch carrier KLM apologized for stranding passengers there this month.

London’s Gatwick and Heathrow airports are asking airlines to cap their flight numbers. Discount carrier easyJet is scrapping thousands of summer flights to avoid last-minute cancellations and in response to caps at Gatwick and Schiphol. North American airlines wrote to Ireland’s transport chief demanding urgent action to tackle “significant delays” at Dublin’s airport.

Nearly 2,000 flights from major continental European airports were canceled one week this month, with Schiphol accounting for nearly 9%, according to data from aviation consultancy Cirium. A further 376 flights were canceled from U.K. airports, with Heathrow accounting for 28%, Cirium said.

It’s a similar story in the United States, where airlines canceled thousands of flights over two days last week because of bad weather just as crowds of summer tourists grow.

The Biden administration scrapping COVID-19 tests for people entering the U.S. is giving an extra boost to pent-up demand for transatlantic travel.

For American travelers to Europe, the dollar strengthening against the euro and the pound is also a factor, because it makes paying for hotels and restaurants more affordable.

In Sweden, lines for security at Stockholm’s Arlanda Airport have been so long this summer that many passengers have been arriving more than five hours before boarding time. So many are showing up early that officials are turning away travelers arriving more than three hours before their flight to ease congestion.

Despite some improvements, the line to one of the checkpoints stretched more than 100 meters on Monday.

The CEO of budget airline Ryanair, Europe’s biggest carrier, warned that flight delays and cancellations would continue “right throughout the summer.” Passengers should expect a “less-than-satisfactory experience,” Michael O’Leary told Sky News.

Some European airports haven’t seen big problems yet but are bracing. Prague’s Vaclav Havel international airport expects passenger numbers to swell next week and into July, “when we might experience a lack of staffers, especially at the security checks,” spokeswoman Klara Diviskova said.

The airport is still short “dozens of staffers” despite launching a hiring campaign at the start of the year, she said.

Labor strife also is causing problems.

In Belgium, Brussels Airlines said a three-day strike starting Thursday will force the cancellation of about 315 flights and affect some 40,000 passengers.