(CNN) — President Trump's recently announced travel ban prevents many non-Americans flying from Europe to the US, but does leaving the UK and Ireland off the restricted list leave a back door open to sneak through?

In force from midnight on March 13, the restriction affects travelers coming from any of the 26 countries making up the Schengen area -- an open border zone within Europe. It also includes people who've been in those countries within the past 14 days.

As soon as the surprise coronavirus-related measure was announced late Wednesday, questions started to be asked about whether travelers could simply hop on a flight or a Eurostar train to the UK and then connect to the States from there, since links between the UK, Ireland and Schengen are currently, for the most part, unrestricted.

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When you're an EU resident traveling within the Schengen zone, your passport doesn't get stamped. So if there's no passport stamp to say you were ever there, who would know?

The answer is, apparently, that the United States would certainly know. And any attempt to lie about it to gain entry would be treated as a crime.

"If you take the Eurostar to London, and then try to fly to the US, you are covered by the suspension having come from a Schengen destination within 14 days -- unless you stay in London for 14 days," advises CNN travel and aviation expert Richard Quest.

The consequences of breaking the ban could be severe.

"An alien who circumvents the application of this proclamation through fraud, willful misrepresentation of a material fact, or illegal entry shall be a priority for removal by the Department of Homeland Security," is the official statement from the White House.

Airlines are going to be double checking passengers' recent movements and will be on the look out for anyone trying to bypass the new rules, according to a spokesperson for London's Heathrow Airport.

CNN understands that passengers will be required to fill out these details on their ESTA -- or Electronic System for Travel Authorization form. Lying on your ESTA form is a criminal offense.

It's not immediately clear what happens if passengers are traveling on a pre-existing ESTA.

"We can confirm airlines will be verifying passengers' immediate travel histories before departure from the UK to ensure travelers can make a safe onwards journey," the Heathrow spokesperson said.

"We continue to work closely with the government, Public Health England, Border Force, and airlines to ensure the safety of our passengers, colleagues and the wider UK."

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Flight operational changes

Travelers are questioning how the new European travel ban will work in actuality. DANIEL LEAL-OLIVAS/AFP via Getty Images

The new travel ban brings with it uncertain times for those hoping to travel between Europe and the United States in the near future.

Even if passengers are US citizens and exempt from the ban, they could struggle to find flights between the Schengen zone and the United States.

Low cost carrier Norwegian has said it's grounding 40% of its long-haul fleet and canceling up to 25% of its short-haul flights until the end of May.

The airline said all routes between London Gatwick airport and the United States will operate "as normal."

"Our goal is to reroute as many of our customers as possible through London during this difficult period," says a Norwegian spokesperson.

Meanwhile, Delta said it will operate nearly a full schedule of flights from continental Europe to US gateways until March 15 "to ensure eligible customers can return to the United States."

From next week the airline said it will fly "a significantly reduced US-Europe schedule while monitoring customer demand."

Delta's change fees have been waived until the end of May.

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United Airlines will also waive fees for travelers, until April 30. Regular scheduling will take place until March 19, after that the airline says it expects to fly daily to Zurich, Brussels, Paris, Amsterdam, Manchester and Edinburgh.

United also expects to run regular flights to Frankfurt and Munich, a less than daily service to Lisbon -- and maintain 18 flights to and from London, and three to Dublin.

Air France plans to continue to serve several airports that are among those approved for health screening.

SWISS also said it was preparing a special reduced flight timetable, and will only serve Chicago and Newark.

The Lufthansa group announced that its airlines will continue to serve US destinations from Germany, Austria, Switzerland and Belgium.

KLM said in a statement that there were plans to "examine on a daily basis whether adjustments to the network are necessary."

The Dutch airline said it plans to "maintain the network to destinations in the US where passengers are screened for the next two weeks as long as possible, also to give customers the opportunity to travel home."

Fear of canceled flights

While US nationals and those exempt from the ban don't have to return to the United States right away, the shaky status of commercial aviation and rising prices meant many have opted to leave as soon as possible -- some via the UK.

Molly Butcher, 56, scrambled from Amsterdam to head to New York via Heathrow on Friday, paying $2,800 to fly a day earlier. Flying direct from the Netherlands would've cost her $6,000.

"We were in Amsterdam and we decided to change 'cause we thought we just wanted to get home just in case he [Trump] changes it and the UK is not exempt anymore," she told CNN.

"We're going to try to get the money back. I talked to several people on the Eurostar today, one family, four of them, paid $7,000."

"On the Eurostar it was pretty full, I'm assuming people were trying to get back out of London 'cause the ban isn't here but it's in Amsterdam and other places."

Julie Blades, 55, traveling to Chicago with her 21-year-old son Jack Colombo, said she also rerouted via London after canceling her scheduled American Airlines flight home from Paris due to leave Saturday.