Facebook is set to take another pounding in Congress on Tuesday as a whistleblower who left with tens of thousands of internal documents told lawmakers how the company pushed for higher profits while being cavalier about user safety.

Frances Haugen, a former product manager on Facebook's civic misinformation team, said the social media giant keeps its algorithms and operations a secret.

"The core of the issue is that no one can understand Facebook's destructive choices better than Facebook, because only Facebook gets to look under the hood," she said in written testimony prepared for the hearing.

"A critical starting point for effective regulation is transparency," she said in testimony to be delivered to a Senate Commerce subcommittee. "On this foundation, we can build sensible rules and standards to address consumer harms, illegal content, data protection, anticompetitive practices, algorithmic systems and more."

In an era when bipartisanship is rare on Capitol Hill, the top Democrat and Republican on the subcommittee agreed on the need for big changes at Facebook.

Subcommittee chair Richard Blumenthal noted that Facebook's leadership had rejected recommendations made to make its sites, which include Instagram, safer.

"There are a lot of teens who are looking in the mirror right now and feeling bad about their self image and their bodies. Mark Zuckerberg should be looking in the mirror," he said in a television interview on Tuesday.

The top Republican, Marsha Blackburn, is expected to say in opening remarks that Facebook turned a blind eye to children below age 13 on its sites. "It is clear that Facebook prioritizes profit over the well-being of our children."

Haugen came forward this week to reveal she was the one who provided documents used in a Wall Street Journal investigation and a Senate hearing on Instagram's harm to teen girls.

Facebook did not respond to a request for comment.

The Journal's stories showed the company contributed to increased polarization online when it made changes to its content algorithm; failed to take steps to reduce vaccine hesitancy; and was aware that Instagram harmed the mental health of teenage girls.

Haugen said Facebook had also done too little to prevent its platform from being used by people planning violence.

Facebook was used by people planning mass killings in Myanmar and the Jan. 6 assault on the U.S. Capitol by supporters of then-President Donald Trump who were determined to toss out the 2020 election results.