In a series of Twitter posts overnight Thursday, Google chief executive Sundar Pichai agreed that "forcing companies to enable hacking could compromise users' privacy."
Pichai acknowledged the "significant challenges" faced by law enforcement fighting crime and terrorism. But he drew a line between tech companies giving up data in compliance with court orders and requiring them to enable hacking of customer devices and data.
"Could be a troubling precedent," he wrote.
WhatsApp chief executive Jan Koum agreed, writing on Facebook that "we must not allow this dangerous precedent to be set. Today our freedom and our liberty is at stake."
A US federal judge on Tuesday ordered Apple to help the FBI crack the encryption on an iPhone linked to the San Bernardino, California, terror attack. The FBI believes there may be data encrypted on the device that could help their investigation.
Apple chief executive Tim Cook refused the judge's order in an open letter posted on the company's website Tuesday.
"The US government has asked us for something we simply do not have, and something we consider too dangerous to create. They have asked us to build a backdoor to the iPhone," Cook wrote. Such a move would "undermine the very freedoms and liberty our government is meant to protect."
The December 2 attack in San Bernardino was carried out by Syed Rizwan Farook and his wife, Tashfeen Malik, at a holiday party at the county office where Farook worked. Fourteen people were killed.
Police killed Farook and Malik later that same day in a shoot-out.
The FBI wants Apple to help it hack into Farook's iPhone by disabling a security feature that destroys data stored on the device after ten failed password entries, so that the agency can program a computer to try all possible passwords until it finds the right one.
The White House Wednesday called the case an "important national priority." Spokesman Josh Earnest downplayed the request, saying investigators were simply asking for a way in to this single device.
But Cook said there was no way to guarantee those limits, and that cracking this device "would undeniably create a backdoor" to all iPhones and other encrypted Apple devices.
The digital privacy group Electronic Frontier Foundation and the leading rights group American Civil Liberties Union said it would help Apple in its legal fight against the order.
Executives from Facebook, Microsoft, and Twitter had yet to comment publicly.
©2016 Deutsche Presse-Agentur GmbH (Hamburg, Germany), Distributed by Tribune Content Agency, LLC.