"People's private messages would be less secure and the real winners would be anyone seeking to take advantage of that weakened security. That is not something we are prepared to do", the company said.
The statement follows Senate hearings in the U.S. where executives from Facebook and Apple defended their privacy practices. In a letter to Facebook CEO Mark Zuckerberg, they insisted that precluding access by law enforcement could hinder efforts to prevent or investigate crimes.
Facebook's response to Barr was released as representatives from the company and Apple were set to appear at a Senate hearing Tuesday on the benefits and risks of encryption. In recent months, Barr has questioned whether encryption - an option to hide the contents of the message from anyone other than the people who sent and received it - may be allowing criminals to evade detection by the authorities.
The report notes how both Apple and Facebook have been on the end of tussles with governments over encryption.
"You're going to find a way to do this or we're going to go do it for you", republican senator Lindsey Graham was quoted as saying by Reuters. Lindsey Graham of SC, the chairman of the Senate Judiciary Committee, as he opened the hearing. "Because this time next year, if we haven't found a way that you can live with, we will impose our will on you", he said.
The government and big tech companies have been on opposite sides of the back door issue since the Federal Bureau of Investigation asked Apple to provide it with a way to break into an iPhone belonging to a mass shooter in 2016. Facebook also plans to extend it to Instagram Direct.
Facebook has hit back at United Kingdom home secretary Priti Patel's calls for a "backdoor" into planned encryption across its messaging apps, saying it would be a "gift to criminals". The goal is to integrate all these services, so users can talk to each other across applications, while delivering "end-to-end" encryption for all their conversations. They asked Facebook to "enable law enforcement to obtain lawful access to content in a readable and usable format". The letter repeatedly emphasized the dangers of child sexual exploitation to justify their stance.
"Our understanding is that much of this activity, which is critical to protecting children and fighting terrorism, will no longer be possible if Facebook implements its proposals as planned", they wrote.
"These exceptional access mechanisms for law enforcement agencies would be the same "backdoors" that provide an opportunity for terrorists, criminals, and other parties to gain unauthorized access", said the letter endorsed by the American Civil Liberties Union, Amnesty International, Human Rights Watch and other organizations and individuals.