At the start of the pandemic, demand for talk therapy apps skyrocketed. Prominent players, like BetterHelp and Talkspace, saw their downloads nearly double throughout the first few months of lockdown in 2020. Now, lawmakers like Sen. Elizabeth Warren (D-MA) are demanding details on how these companies protect the privacy of their users.

In letters to BetterHelp and Talkspace executives on Thursday, Warren — along with Sens. Cory Booker (D-NJ) and Ron Wyden (D-OR) — called on the mental health companies to explain how their apps collect and use data obtained from their patients. Specifically, lawmakers requested information on the apps’ relationships with online advertisers, data brokers, and social media platforms like Facebook as well as how those relationships are disclosed to users.

Reviewing the companies’ privacy policies, the senators wrote that “unfortunately, it appears possible that the policies used by your company and similar mental health platforms allow third-party Big Tech firms and data brokers, who have shown remarkably little interest in protecting vulnerable consumers and users, to access and use highly confidential personal and medical information.”

The letter follows a report published in May by the Mozilla Foundation, which warned consumers that online talk therapy apps could be profiting off of their mental health data. While both BetterHelp and Talkspace promise not to sell a user’s medical data without their consent, the researchers determined that personal information — like a patient’s name, phone number, and email — could still be sold or accessed by third parties for advertising and marketing purposes.

While personal information isn’t as sensitive as medical data, it can still reveal intimate insights into a user’s life. For example, Jezebel reported in 2020 that BetterHelp shared the metadata of messages between a patient and therapist with Facebook. The data does not include the contents of these messages but could alert online marketers to how frequently and where a user could be using the app.

“Even though you claim this data is anonymized, it can still provide third parties with important and identifying information,” the senators wrote, citing a 2019 MIT Technology Review study on how multiple pieces of anonymized data could be used to construct individual user identities.

Warren’s letter comes amid a broader push to regulate data sales in the US. The House Committee on Energy and Commerce is set to mark up sweeping privacy legislation on Thursday. It’s the closest lawmakers have come to a deal over the last few years. Last week, Warren introduced her own measure that would ban the sale of location and sensitive health data as the Supreme Court is poised to roll back Roe v. Wade.

While the pandemic played a major role in popularizing therapy apps, the companies also paid popular influencers like Shane Dawson and Philip DeFranco to advertise their apps on social media years prior. That advertising campaign erupted in controversy in 2018 after fans accused the YouTubers of profiting off of their audience’s mental health issues with apps accused of hiring unqualified therapists, as reported by The Atlantic.