The secure messaging app Signal has threatened to stop operating in the UK if new legislation weakens encryption.
Meredith Whittaker, president of Signal, told the BBC that the company would "absolutely, 100 percent walk" if the Online Safety Bill required it to lessen the privacy of its messaging system.
According to the government, its proposal did not "ban end-to-end encryption.".
The Boris Johnson-introduced bill is currently being debated in Parliament.
According to critics, the new law may require companies to scan messages on encrypted apps for terrorism-related or child sex abuse material.
This has alarmed companies whose business it is to facilitate secure, private communication.
A UK company called Element, whose clients include the Ministry of Defense, told the BBC that the plan would cost them business.
In the past, WhatsApp has assured the BBC that it will not compromise security for any government.
Government officials and well-known child protection organizations have long argued that encryption makes it more difficult to stop the growing problem of online child abuse.
The Home Office issued a statement saying, "It is important that technology companies make every effort to ensure that their platforms do not become a breeding ground for pedophiles.".
The bill also stated that end-to-end encryption was not prohibited but that technological advancements should not be made in a way that compromises public safety, particularly children's online safety.
"We can and must have both privacy and child safety; there is no trade-off to be made. ".
However, Ms. Whittaker told the BBC that believing we can have privacy "but only for the good guys" is "magical thinking.".
"Either encryption protects everyone, or it is broken for everyone," she continued. ".
She claimed that a form of this magical thinking was "embodied" in the Online Safety Bill.
On the Google Play store alone, more than 100 million people have downloaded Signal.
End-to-end encryption is used, a system that scrambles messages so that not even the company running the service can decipher them.
Users of the app, which is run by a non-profit organization with a Californian headquarters, include journalists, activists, and politicians.
In addition to Facebook and Telegram, WhatsApp also uses end-to-end encryption, as does Apple's iMessage service.
After receiving criticism, Apple dropped plans to implement a system that would have checked messages sent from phones and other devices for images of child abuse before encrypting them.
Some have claimed that this method, known as client-side scanning, will eventually be required of tech companies; however, detractors claim it effectively defeats the purpose of encryption.
Everyone's phone would essentially become a "mass surveillance device that phones home to tech corporations, governments, and private entities," according to Ms. Whittaker.
In order to allow for the scanning of private messages, Ms. Whittaker claimed that "back doors" would be exploited by "malignant state actors" and "create a way for criminals to access these systems.".
She responded to the BBC's question about whether the Online Safety Bill might jeopardize their ability to provide a service in the UK by saying, "It could, and we would absolutely 100% walk rather than ever undermine the trust that people place in us to provide a truly private means of communication.
"We have never compromised on our commitment to privacy, and we never will. ".
The threat of mandatory scanning, according to Matthew Hodgson, chief executive of Element, a British secure communications company, would cost him clients.
Customers would presume that any secure communication device coming from the UK would "necessarily have to have backdoors in order to allow for illegal content to be scanned," the speaker claimed.
A government bill could also undermine the security assurances provided to clients at the MoD and other delicate areas of government, creating "a very surreal situation," he continued.
He added that the business might have to stop providing some services.
No one, according to Ms. Whittaker, "does not want to protect children." She continued, "Some of the stories that are invoked are harrowing. ".
When asked how she would respond to claims that encryption shields abusers, Ms. Whittaker said she thought the majority of abuse occurred in families and communities, where she thought efforts to stop it should be concentrated. .
She cited a paper written by Professor Ross Anderson in which he argued for increased funding for child protection services and cautioned that "the idea that complex social problems are amenable to cheap technical solutions is the siren song of the software salesman."