Child-protection organizations say Facebook’s decision to strongly encrypt messages will give offenders a place to hide.
The company is moving ahead with plans to implement the measure on Facebook Messenger and Instagram Direct.
But more than 100 organizations, led by the NSPCC, have signed an open letter warning the plans will undermine efforts to catch abusers.
Home Secretary Priti Patel said she “fully supported” the move.
In a statement to the BBC, she said: “Tech companies like Facebook have a vital responsibility to balance privacy with the safety of vulnerable children.”
“Following my letter to Mark Zuckerberg, I met with Sheryl Sandberg and emphasized that Facebook’s encryption plans cannot be allowed to hamper their ability to protect young people from paedophiles online. We have also submitted detailed evidence to the US Senate about these concerns.
“I fully support the continued efforts of the NSPCC and children’s charities around the world to engage Facebook on this issue.”
End-to-end encryption, already used on Facebook-owned WhatsApp, means no-one, including the company that owns the platform, can see the content of sent messages.
Those signing the letter say Facebook has failed to address concerns about child safety. The missive urges the company to stop the rollout of its plans until “sufficient safeguards” are in place.