A group of technology companies and organizations have sent an open letter condemning the UK Government Communications Headquarters (GCHQ) proposal to secretly add law enforcement to encrypted chats.

The letter from the Open Technology Institute—along with 47 signatories including Google, Apple and WhatsApp—details concerns about threats to cybersecurity and human rights that this proposed action creates.

The proposal suggests adding a “ghost” user to encrypted group chats or calls. This would “enable the ghost user to see the plain text of an encrypted call or chat without notifying the participants.” The letter sets out the security risks that the proposal creates, undermining the authentication process and increasing risks that the platforms could be misused or abused. Additionally, the letter claims the proposed changes could unintentionally create vulnerabilities that would affect every user of the application.

The letter, sent last week and made public Thursday, also focuses on the issue of trust between the user and the service provider, arguing that, “any proposal that undermines user trust penalizes the overwhelming majority of technology users while permitting those few bad actors to shift to readily available products beyond the law’s reach.”

The groups urge GCHQ to abandon the ghost proposal and to avoid similar alternative approaches.