Tips for Travelers Entering the U.S. Now: Check Your Visa, Turn Off Your Phone

With increasing news reports of travelers being denied entry, understanding what might prompt extra scrutiny is key. Here’s what to know.

At airports and land borders across the country, tourists and other visitors coming to the United States have reported being caught up in the Trump administration’s campaign of “enhanced vetting.” Even legal immigrants, like green card holders, and naturalized citizens have been pulled aside for additional questioning and searches.

This has prompted questions about best practices for crossing into the United States, travelers’ rights at the border, and the legality of device and luggage searches.

Here are some things to know before you visit or return to the United States, as a tourist, legal resident or citizen.

“We’ve seen people detained just for saying they’re ‘Open to Work’ on LinkedIn,” said Michael Wildes, the New Jersey-based immigration lawyer who handled Melania Trump’s immigration to the United States. “That serves as proof that they’re not just going to Disneyland or to a wedding.”

Cheryl David, an immigration lawyer in New York City, stressed that no rules have changed when it comes to entering the United States, but she said, there is now a clear “zero tolerance policy.”

This year, the family of Becky Burke, a 28-year-old British tourist, said she was stopped at the U.S. border in Washington State on her way to a work-exchange trip, where she planned to trade house chores for free accommodations. While no money changed hands, those arrangements could still be seen as work, which would violate the terms of a tourist visa. Ms. Burke ended up detained for 19 days before she was deported to Britain.

While detaining prospective tourists is rare, deportations because of incorrect travel documentation is not.

Cellphones and other devices can be subject to search at the border and a traveler’s ability to push back depends on whether they are a citizen of the United States or not.

If questions arise regarding passengers’ travel documents, border officials can pull them out of line and submit them to additional screening, at which point luggage and electronic devices such as laptops and cellphones can be searched.

Even green card holders and naturalized citizens may be subject to more screening.

U.S. citizens and lawful permanent residents cannot be denied entry to the country for refusing to hand over their devices, but such a refusal could still lead to a longer customs process, the A.C.L.U. said.

Catherine, 67, a naturalized citizen who moved to the United States 45 years ago, said she had never been selected for additional questioning when coming through immigration, but that since the start of the Trump administration she has been stopped twice for reasons that remain unclear to her. Catherine asked to be identified by only her middle name, because of her fears that her naturalized status could be revoked for speaking out.

Most recently, Catherine was returning from Argentina when she and her husband were stopped at an airport in Dallas. Border control there was automated, with passengers scanning passports to get through gates, but when it came time to take a photograph, a big red X flashed on the screen for Catherine. Her husband spoke to border officials, and the couple eventually got through.