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 naturalised citizens have been pulled aside for additional questioning and searches.

This has prompted questions about best practices for crossing into the United States, travellers’ 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.

ARE YOU A VISITOR WITH A VISA OR ESTA? IT SHOULD ALIGN WITH YOUR TRAVEL PLANS

According to the American Civil Liberties Union (ACLU), US border officials have “wide-ranging discretion” to deny entry. That decision can be made based on suspicion that the person is entering the country for a purpose other than what their visa or Electronic System for Travel Authorization (ESTA) says — for example, they have a tourist visa, but it seems like they may be planning to work.

“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 US 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.

EVEN CITIZENS SHOULD PREPARE FOR ADDITIONAL SCREENING

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 cell phones can be searched.

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

US 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 ACLU said.

Catherine, 67, a naturalised 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 naturalised 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.

TRAVELLERS’ SOCIAL MEDIA, TEXT CHATS AND OTHER HISTORY ON THEIR DEVICES CAN BE SEARCHED

Because border control technically exists outside the United States, travellers with visas or those with ESTAs have limited ability to push back against searches of their electronic devices, according to the ACLU, and if they do, they risk being denied entry.

There are generally two types of searches of an electronic device: manual and advanced, said Tom McBrien, a lawyer with the Electronic Privacy Information Center, an internet privacy nonprofit in Washington. Manual searches involve looking through an unlocked phone. Courts have generally seen this as equivalent to going through luggage and have allowed manual searches to proceed without obtaining a warrant, Mr. McBrien said.

An advanced, or “forensic” search, involves hooking up an external device to your phone to scan its contents. Some federal districts require a warrant for this, while others do not, Mr McBrien said.

Mr McBrien and other privacy experts recommend deleting anything you wouldn’t want someone to read or see from your device before your arrival.

Mr McBrien also said that he recommends his clients disable the Face ID or Touch ID features on their iPhones, so that it takes more than an officer waving a phone in front of their face or placing their finger on it to open it. Even better, he said, is to turn off your phone before going through border control, because phones tend to require your full passcode when turned back on.

If you refuse to unlock your phone when asked, authorities can seize it and will most likely need to obtain a warrant to open it, he added. However, visitors can be denied entry to the United States for refusing to unlock their phone.

However, Mr Wildes, the New Jersey-based immigration lawyer, said that the main thing border patrol officers look for is consistency.

If a forensic search shows a deactivated social media account, officials may ask for it to be reactivated, Mr. Wildes said. If an email account was recently deleted, they can request to access it.

Social media has become a major issue, he added, for “so many people who don’t realise how actionable it can be.”

Ms David, the immigration lawyer, recalled a client with a student visa who was denied entry to the United States during the Biden administration because he had photos on his phone of him posing with guns, which officials interpreted as a threat to the United States, she said.

The best thing to do, Mr Wildes said, is to be honest and also be aware of the laws.

If you do get in trouble at the border, he said, the best move for visitors may be to withdraw your intention to enter the United States. In most cases, you can return to your home country.

This article originally appeared in The New York Times.

Tips for travellers entering the US now: Check your visa, turn off your phone