Wray, addressing a crowd of law enforcement and child protection officials at the Department of Justice in Washington, said that Facebook’s plan would produce “a lawless space created not by the American people or their representatives but by the owners of one big company.”

Facebook intends to add encryption of wide swathes of communications on its platform.

His speech, which came ahead of an address on the same topic by Attorney General William Barr, ratchets up the pressure on Facebook as the U.S. and allied governments renew their push to weaken the digital protections around the messages billions of people exchange each day.

The Justice Department’s No. 2 official estimated that tips to law enforcement about possible child exploitation could drop by as much as 70 percent if Facebook encrypts its messaging program.

Facebook reported 16 million child-exploitation tips last year, Deputy Attorney General Jeffrey Rosen said. By contrast, Apple, which already uses end-to-end encryption on its messenger, reported 43 tips last year.

The Justice Department event is part of a renewed push by the American, Australian, and British governments to force tech companies to help them circumvent the encryption that helps keeps digital communications secure.

Debates over encryption have been rumbling for more than 25 years, but officials’ anxiety has increased as major tech companies move toward automatically encrypting the messages on their platforms and the data held on their phones.

In the past, officials have cited the threat of terrorism to buttress their campaigns again encryption. But as the Islamic State and other extremist groups fade from the headlines, governments are trying a different tack, invoking the threat of child abuse to argue for “lawful access” to these devices.

Facebook’s privacy-focused move, announced by founder and CEO Mark Zuckerberg this year, is causing particular consternation because the platform is the source of millions of tips to authorities about child abuse images every year.

Zuckerberg, speaking on the company’s weekly internal Q&A livestream, defended the decision, saying he was “optimistic” Facebook would be able to identify predators even in encrypted systems using the same tools it used to fight election interference.

“We’re going to lose the ability to find those kids who need to be rescued,” Wray said. “We’re going to lose the ability to find the bad guys.”

Many people have applauded Facebook’s push for privacy and security. Academics, experts, and privacy groups have long worried that circumventing the protections around private communications would open dangerous vulnerabilities that could make the entire internet less safe, and leave billions of users exposed to abusive surveillance.

Wray steered clear of making any specific proposal, saying that “companies themselves are best placed” to offer a way for law enforcement to get around encryption.