Following a recent investigation by The Markup, Sen. Elizabeth Warren and colleagues are questioning tax filing companies, Meta, and Google about how users’ sensitive financial information was shared with the tech companies.

Last month, The Markup, in partnership with The Verge, revealed how major tax filing companies such as H&R Block, TaxAct, and TaxSlayer have been transmitting filers’ personal data to Facebook through code called the Meta Pixel. 

The pixel is widely used by businesses to gather information about their website visitors, which can then be used to measure advertising effectiveness and target new ads. In this case, the data sent to Facebook included not only tax filers’ names and email addresses but also, in some cases, even users’ income, filing status, refund amounts, and dependents’ college scholarship amounts. The Markup originally discovered the sharing of taxpayer’s information using data contributed by participants in the Mozilla Rally project. 

One of the companies, TaxAct, also transmitted some of the same data to Google through the tracking tool Google Analytics.

After the investigation was published, the tax filing companies either removed their Meta Pixels or changed the pixels’ settings to capture less data. Lawyers representing people who used the H&R Block website subsequently filed a proposed class action lawsuit against Meta in federal court, alleging that the company broke contractual promises to users.

Citing The Markup’s investigation, Warren and other federal lawmakers sent letters requesting more information about the data collection. The letters were addressed to the heads of H&R Block, Tax Act, TaxSlayer, Intuit, Meta, and Google. Warren, along with California representatives Katie Porter and Brad Sherman, led the outreach, while Senators Tammy Duckworth, Sheldon Whitehouse, Bernie Sanders, Richard Blumenthal, and Ron Wyden also signed the letters.

The letters describe the tax sites’ tracking as “an appalling breach of users’ trust and a potentially illegal misuse of sensitive taxpayer data.” 

“If The Markup’s reporting is accurate, taxpayers deserve justice for this abuse of their private tax information, and we hope that the IRS and if merited, the Department of Justice, will act to impose appropriate penalties on companies,” the letter informs the tax preparation companies.

The letters go on to ask for detailed information about what data was gathered, for how long, whether data was collected based on the default settings of the trackers or customization made by the sites, and whether the tax preparation companies intend to use mandatory arbitration clauses to block any civil suits stemming from the disclosures. The lawmakers requested  responses from companies by Jan. 3.

TaxSlayer, TaxAct, and Google didn’t immediately respond to The Markup’s requests for comment. Dale Hogan, a spokesperson for Meta, said in an email that it is against Meta’s policies to send sensitive information through its tools. “Doing so is against our policies and we educate advertisers on properly setting up Business tools to prevent this from occurring,” he said. “Our system is designed to filter out potentially sensitive data it is able to detect.”

Rick Heineman, a spokesperson for TurboTax parent company Intuit, reiterated a previous statement that Intuit “does not share tax return information with social media platforms, including Meta (Facebook), for marketing or any other purpose,” and that the company is in compliance with the law.

Angela Davied, a spokesperson for H&R Block, said the company “takes our clients’ privacy seriously” and would review the letter and respond.

Unlike in many other countries, where the government handles tax filing calculations, the United States’ system relies heavily on third-party tax preparers. This structure has led to the creation of a multibillion-dollar industry that Warren has frequently criticized. In July, Warren and Porter introduced legislation that would direct the Internal Revenue Service to build its own free tax filing service.

In the letters, the lawmakers again call for the IRS to intervene by creating its own filing system for taxpayers.

“These shocking reports of breaches of taxpayer privacy by tax preparation companies using Meta’s tools underscores the need for the IRS to provide its own free tax filing software,” the legislators wrote.