*This is reported by Yahoo News.

Several European countries have updated their travel guidance for citizens visiting the U.S., including recent guidance for transgender and nonbinary travelers.

It’s common for countries to issue travel advisories or warnings for things like crime levels, terrorism threats, current conflicts, health concerns or natural disasters.

The U.S. issues its own travel advisories for Americans traveling abroad, but a number of other countries are doing the same for the U.S. These new advisories come as the Trump administration is tightening U.S. borders, cracking down on undocumented migrants and implementing a new federal policy to recognize male and female, rather than gender identity, as the only legitimate sexes.

Canada, the United Kingdom and Germany have also updated their travel guidance for their citizens planning to travel to the United States after several tourists were detained by U.S. immigration authorities in recent months.

Travelers from many European countries and the U.K. can travel to the U.S. for business or tourism and stay for up to 90 days without a visa under the Department of Homeland Security’s Visa Waiver Program. But several travelers from countries within the program — like Canada, Germany, the U.K. and France — have been stopped and detained by U.S. immigration authorities within recent months.

Here’s what has transpired.

Nations with LGBTQ advisories for the U.S.

President Trump signed an executive order in January that says the federal government only recognizes two biological sexes: male and female. Per that order, a visitor applying for a visa or an Electronic System for Travel Authorization (ESTA) must declare their sex assigned at birth on the application forms.

European allies, including Denmark, Finland, Germany, Ireland, the Netherlands and Portugal, issued guidance that advises transgender and nonbinary travelers to contact the U.S. Embassy in their respective countries for more information on how to proceed if they wish to travel to the U.S.

Nations with other travel advisories for the U.S.

Canada

Recent tensions between the U.S. and Canada have risen over Trump’s trade war, not to mention his musings that he would make the northern ally the U.S.’s 51st state. Canada added new information under its U.S. travel advice page regarding the requirements for foreign nationals visiting for more than 30 days.

“Canadians and other foreign nationals visiting the United States for periods longer than 30 days must be registered with the United States Government. Failure to comply with the registration requirement could result in penalties, fines, and misdemeanor prosecution,” according to the Canadian government’s website.

The rule, enforced starting April 11, comes as part of an executive order signed by Trump, which requires all visitors staying for 30 days or longer to register with the U.S. government.

Germany

Last month, Germany updated its guidelines for its citizens looking to travel to the U.S. The European nation is investigating the cases of three of its citizens being denied entry and placed into detention by U.S. immigration authorities.

“Neither a valid [ESTA] authorization nor a valid U.S. visa constitutes a right to entry into the USA,” according to a translation of the German Foreign Office website. “The final decision regarding entry is made by the U.S. border official. It is recommended that you bring proof of your return journey (e.g., flight booking) upon entry.”

The office also warns of potential legal consequences. “Criminal records in the United States, false information about the purpose of their stay, or even a slight overstay of their visa upon entry or exit can lead to arrest, detention, and deportation.”

Two German nationals were detained in January as they were separately trying to cross the San Ysidro border between San Diego and Tijuana, Mexico, the New York Times reported. They have since returned to Germany with their cases resolved. A third remaining case involves a German national — who is a legal permanent U.S. resident who received a green card residency permit in 2008 — who was detained by ICE at Boston International Airport on March 7. He is now being held at the Wyatt Detention Center in Central Falls, R.I., NBC News reported.

The United Kingdom

The U.K. Foreign Office has updated guidance on its website in recent weeks for its citizens traveling to the U.S. It currently states, “You should comply with all entry, visa and other conditions of entry. The authorities in the U.S. set and enforce entry rules strictly. You may be liable to arrest or detention if you break the rules.”

Archived versions of the same website did not include potential legal consequences at the beginning of February and only stated, “The authorities in the U.S. set and enforce entry rules,” Reuters reported.

The Foreign, Commonwealth and Development Office did not explain the reason for the change.

The update comes around the same time a British tourist said she was held for more than two weeks in Washington state. Becky Burke, a 28-year-old from Wales, was backpacking through North America when she was allegedly denied entry into Canada on Feb. 26 “due to an incorrect visa,” according to a Facebook post by her father, Paul Burke. She was subsequently denied reentry into the U.S. and was detained at a facility in Tacoma, Wash.

Burke had stayed with a host family in Oregon, where she performed chores in exchange for food and lodging. She was told she violated her visa even though she was never paid. Travelers using a temporary visitor visa cannot accept work or employment in the country. Burke was repatriated back to the U.K. on March 18, according to U.S. Immigration and Customs Enforcement.

New Zealand

Last November, New Zealand updated its travel guidelines to the U.S. to “Exercise increased caution in the United States of America (US) due to the threat of terrorism (level 2 of 4).” The nation’s government travel website points to higher active shooter incidents and violent crime in the U.S. compared to New Zealand.