Smartphones are becoming targets of customs agents at airports, including San Francisco International.
Aaron Gach, a San Francisco artist and professor, said customs agents at SFO demanded to search his iPhone after a recent trip.
"I eventually consented, unlocked my phone and handed it over, which they searched out of my sight," Gach said.
The ACLU said phone searches are happening more frequently and believes the law surrounding such searches is murky.
Mike McCarron, an airport security consultant, explained to NBC Bay Area what authorities are looking for in searches.
"They were saying it's a random search -- they may be looking for a specific name, for someone who fits a specific profile," McCarron said.
The ACLU said it is now working with Gach and believes customs officers may be violating citizens' privacy rights.
"It's certainly a situation where if you're carrying sensitive information, your company's intellectual property or your personal e-mail, or something you're worried about being exposed, you might want to consider not carrying that information across the border," said Chris Conley, an ACLU policy attorney.