The boss of Apple has warned against giving spies a "back door" to reading people's emails because weakening data security could help criminals.
Tim Cook said any attempt to weaken encryption could have "very dire consequences", harming consumers by making their data less secure.
Under proposals in Theresa May's Investigatory Powers Bill, communications firms will be legally required to help spies hack into suspects' smartphones and computers.
Domestic providers will be obliged to assist intelligence agencies when they are given warrants to carry out equipment interference .
The technique allows authorities to interfere with electronic devices in order to obtain data and can range from remotely accessing a computer to covertly downloading the contents of a mobile phone.
It is seen as an increasingly crucial tool as advanced encryption makes intercepting targets' communications more difficult.
There are also fears in technology circles that the proposals will hit services offering "end-to-end encryption" such as WhatsApp and Apple's iMessage, despite the Home Secretary's assurances that the legislation "will not ban encryption or do anything to undermine the security of people's data".
The proposed new laws could impose obligations on telecommunications providers requiring them to remove "electronic protection" applied to "communications or data".
In an interview with the Daily Telegraph, Mr Cook said: "To protect people who use any products, you have to encrypt. You can just look around and see all the data breaches that are going on.
"These things are becoming more frequent. They can not only result in privacy breaches but also security issues. We believe very strongly in end-to-end encryption and no back doors."
The technology giant's chief executive warned: "We don't think people want us to read their messages. We don't feel we have the right to read their emails.
"Any back door is a back door for everyone. Everybody wants to crack down on terrorists. Everybody wants to be secure. The question is how. Opening a back door can have very dire consequences."
He added: "It's not the case that encryption is a rare thing that only two or three rich companies own and you can regulate them in some way.
"Encryption is widely available. It may make someone feel good for a moment but it's not really of benefit. If you halt or weaken encryption, the people that you hurt are not the folks that want to do bad things. It's the good people. The other people know where to go."
But he said he was "optimistic" that the Government would change its approach: "When the public gets engaged, the press gets engaged deeply, it will become clear to people what needs to occur.
"You can't weaken cryptography. You need to strengthen it. You need to stay ahead of the folks that want to break it."