Since Edward Snowden revealed the full scale of the mass surveillance being carried out by the National Security Agency (NSA) at the behest of the U.S. government, encryption has been a hot button issue for tech companies. Apple and Google led the wave by encrypting all iOS and Android smartphones, and both companies have stood up to the federal government multiple times to defend encryption and the privacy of their millions of users.

“We are challenging the FBI’s demands with the deepest respect for American democracy and a love of our country.”

Apple’s CEO Tim Cook has been more vocal than most, and his stance on privacy and encryption is nothing short of revolutionary. He is the first major tech CEO to stand up and declare that encryption and privacy on the Internet is a “fundamental right.” He’s led countless discussions on the importance of encryption and warned about the dangers of creating backdoors in technology products for the government — and the bad guys, Cook reasons — to get in when they please. Now, Cook is taking the battle for privacy and encryption on the Internet to an entirely new level.

He has denied a court order and an FBI demand to disable the iPhone’s auto-erase function, which removes all data from a device after 10 failed attempts to break into it. But it’s not just any phone that has Cook fuming: It’s the phone of Syed Rizwan Farook, the San Bernadino shooter who gunned down 14 people and is suspected of having ISIS sympathies. The decision to say no to the court’s order to reveal the contents of Farook’s phone is a very serious one, which will likely have major consequences for the tech world and for Apple.

In a brave letter to Apple’s customers, Tim Cook explains why he opposes the court’s order and levels with users about the importance of taking a stand for encryption and privacy. He states that the FBI is asking “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 adds that while Apple has worked closely with the FBI to try and find out more information about “this horrible crime,” Apple cannot and will not create a backdoor on the iPhone.

“In the wrong hands, this software – which does not exist today — would have the potential to unlock any iPhone in someone’s physical possession,” he writes. “We are challenging the FBI’s demands with the deepest respect for American democracy and a love of our country. We believe it would be in the best interest of everyone to step back and consider the implications.”