A federal judge in Boston on Thursday heard arguments challenging the U.S. government’s legal authority to search international travelers’ phones and laptops at the airport without a warrant or without probable cause to suspect wrongdoing.

“The traditional powers of the government to search people’s things when they’re entering the country might make sense if we’re talking about a suitcase, but they don’t make sense with our cellphones and laptops, which contain our emails and our browsing history and our photographs, and they’re truly a window to the soul,” said Adam Schwartz, a senior lawyer for the Electronic Frontier Foundation, which brought the lawsuit on behalf of 11 travelers. “The government has no business looking at this information unless they can persuade a judge they have probable cause there’s a crime afoot.”

U.S. Department of Justice attorney Michael Drezner, representing the government, said no court has ever required probable cause or a warrant for any border search of a person or property. “They’re bringing a claim that’s breathtaking in scope and would undermine the authority of border officers that’s been established for centuries,” Drezner said in court.

The American Civil Liberties Union and the Electronic Frontier Foundation in September 2017 sued the heads of the Department of Homeland Security, U.S. Customs and Border Patrol and U.S. Immigration and Customs Enforcement. They argued that searching travelers’ electronic devices without a warrant or any reason for suspicion was an unconstitutional search and seizure and a threat to personal privacy.

The plaintiffs in the case, Asaad v. McAleenan, are 10 U.S. citizens and a lawful permanent resident who had their devices searched at the border. Four had their property held by the government for weeks or months.

Those with Massachusetts ties include Ghassan and Nadia Alasaad, a married couple living in Revere. He is a limousine driver; she is a nursing student. Jérémie Dupin is a Haitian national and a lawful permanent resident of the U.S. who lives in Massachusetts and works as a journalist. Zainab Merchant is a writer and a graduate student in international security and journalism at Harvard University.

One plaintiff had journalism notes on their device; another had attorney-client privileged correspondence.

“Today’s electronic devices contain troves of data and personal information that can be used to assemble detailed, comprehensive pictures of their owners’ lives,” attorneys for the ACLU and EFF argued in their complaint. “Because government scrutiny of electronic devices is an unprecedented invasion of personal privacy and a threat to freedom of speech and association, searches of such devices absent a warrant supported by probable cause and without particularly describing the information to be searched are unconstitutional.”

Esha Bhandari, an attorney for the ACLU, said in court that modern technology raises “unique and unprecedented privacy concerns,” since cellphones contain private information, and it is not practical for travelers to travel without their cellphones.

The ACLU and EFF say the federal agencies have asserted authority improperly to search travelers’ devices for reasons unrelated to border security — for example, to investigate bankruptcy or environmental protection cases or to find information about a traveler’s family member or colleague.

In fiscal 2018, which ended in September 2018, the government conducted 33,000 searches of travelers’ electronic devices at the border, generally at airports or land crossings.

The U.S. government says it does not need a warrant or probable cause to conduct a search at an international border because the government has a national security interest in knowing who and what is coming into the country and preventing contraband from entering.

Drezner said government’s interests in national security and preventing violations of federal law outweigh travelers’ privacy interests.

The government’s briefs say border searches of devices have turned up digital contraband — things like child pornography — as well as evidence of illegal activity, like drug trafficking and firearm smuggling.

Both sides entered motions for summary judgement, asking the court to rule in their favor without a trial.

U.S. District Court Judge Denise Casper said she will take the matter under advisement. Whichever ways she rules, the case is likely to be appealed to a federal Appeals Court.