A plan to force visitors to turn over their social media passwords to Homeland Security will pose dangers to civil liberties and cybersecurity, according to a trade industry group that represents companies like Google and Facebook.
In a statement to Homeland Security Secretary John Kelly, the Computer & Communications Industry Association joined dozens of academics and civil rights groups to oppose the plan, which would allow border guards to ask visitors to provide passwords and social media profiles before they could enter the country.
“This proposal would enable border officials to invade people’s privacy by examining years of private emails, texts, and messages. It would expose travelers and everyone in their social networks, including potentially millions of U.S. citizens, to excessive, unjustified scrutiny,” said the statement.
The letter also warned that letting border agents search social media profiles could trigger similar measures in other countries, forcing Americans to hand over social media accounts to foreign governments when they travel.
Get Data Sheet, Fortune’s technology newsletter
The issue of social media at the border has been a hot topic since a new form at the U.S. border began asking visitors to disclose their presence on sites like Facebook (fb) and Twitter (twtr) late last year. While such disclosures are now voluntary, critics fear they will soon become mandatory, and be expanded to included Americans as well as non-citizens.
The controversy is also fueled by the fact that people enjoy very few privacy rights at the border, where agents are charged with keeping dangerous people and contraband out of the United States. As Fortune explained earlier this month, Americans are not obliged to reveal social media or other online information to the U.S. Customs and Border agency—but refusing to do so can lead border agents to them travelers or to confiscate their devices for a period of time. But if a visitor refuses to supply such information, agents can refuse to admit them altogether.
Meanwhile, U.S. Senator Ron Wyden (D-Or) has said he will introduce legislation to prevent border agents from asking for American’s social media information, and to strengthen Fourth Amendment protections at the border.
Other signatories on the letter to Kelly include Human Rights Watch, the Electronic Frontier Foundation, and Reporters Without Borders.