Tech companies including Apple, Facebook, Google and Microsoft joined Internet security experts and civil liberties organizations this week to draft a letter to President Obama warning that a “backdoor” for U.S. law enforcement could also serve as a backdoor for hackers and other governments. The Obama administration has been considering whether companies should only be allowed to use encryption that provides law enforcement with unscrambled access (or a “backdoor”). Critics are concerned about weakening encryption tech that protects Internet communications.

“We urge you to reject any proposal that U.S. companies deliberately weaken the security of their products,” the letter stated. “We request that the White House instead focus on developing policies that will promote rather than undermine the wide adoption of strong encryption technology.”

Numerous tech companies have been introducing encryption that makes it difficult for the government to monitor communications without going directly to companies’ customers, a move that has been criticized by some in law enforcement.

“The White House is weighing a proposal in which parts of the key to unlock digital encryption would be held by the government, and part would be held by the companies,” reports The New York Times.

“The letter was signed by more than 140 tech companies and dozens of civil liberty, human rights, and press freedom groups like the Electronic Frontier Foundation, Human Rights Watch and the Reporters Committee for Freedom of the Press. It was also signed by some 60 security and policy experts.”

FBI Director James B. Comey has been a vocal critic of tougher encryption. “Sophisticated criminals will come to count on these means of evading detection,” he said, following encryption announcements made last fall by Apple and Google. “It’s the equivalent of a closet that can’t be opened. A safe that can’t be cracked. And my question is, at what cost?”