A group of lawmakers led by Massachusetts Democratic Sen. Elizabeth Warren are calling on the Biden administration to investigate how tax prep software companies may have illegally shared customer data with tech platforms Google and Meta.

In a letter to Attorney General Merrick Garland, Federal Trade Commission Chair Lina Khan, IRS Commissioner Daniel Werfel and Treasury Inspector General for Tax Administration J. Russell George, the lawmakers laid out key findings from their own probe expanding on reporting from The Markup and The Verge, which initially revealed the data sharing. The FTC declined to comment on the letter and the other agencies named did not immediately respond to a request for comment.

In a story published last year, the publications jointly reported that tax prep software companies TaxSlayer, H&R Block and TaxAct had shared sensitive financial information with Meta’s Facebook through a piece of code known as a pixel. The report found that Meta pixel trackers sent names, emails and income information to Meta, in violation of the platform’s policies.

The report also found that TaxAct had sent similar information to Google through its analytics tool, but that information did not include names.

After the initial report, Meta and Google both told CNBC they have policies against customers or advertisers sending them sensitive or identifying information. Some statements the tax prep companies provided to the publications at the time seemed to indicate the data sharing was done accidentally.

In a Wednesday statement, a Google spokesperson said the company has “strict policies and technical features that prohibit Google Analytics customers from collecting data that could be used to identify an individual. Site owners – not Google – are in control of what information they collect and must inform their users of how it will be used. Additionally, Google has strict policies against advertising to people based on sensitive information.”

“We’ve been clear in our policies that advertisers should not send sensitive information about people through our Business Tools,” a Meta spokesperson said in a statement. “Doing so is against our policies and we educate advertisers on properly setting up Business tools to prevent this from occurring. Our system is designed to filter out potentially sensitive data it is able to detect.”

H&R Block said in a statement that the company “takes protecting our clients’ privacy very seriously, and we have taken steps to prevent the sharing of information via pixels.”

The other companies mentioned did not immediately respond to requests for comment.

Building on the original reporting, the group of seven lawmakers opened their own probe into the extent of the data sharing. Among their findings released Wednesday, the lawmakers said that millions of taxpayers’ information had been shared with Big Tech firms through the tax prep software and that both the tax prep companies and tech firms were “reckless” in how they handled sensitive information. Although the companies said information shared would have been anonymous, the lawmakers found that experts believed it wouldn’t be hard to connect the data to individuals.

Sens. Ron Wyden, D-Ore., Richard Blumenthal, D-Conn., Tammy Duckworth, D-Ill., Bernie Sanders, I-Vt., Sheldon Whitehouse, D-R.I., and Rep. Katie Porter, D-Calif., joined Warren in the investigation and letter.

While the tax prep companies installed Meta’s and Google’s tools without fully understanding the privacy implications, according to the lawmakers, the two tech platforms failed to provide enough information about how they would collect and use the information gathered through their tools. Although Meta and Google both said they have filters to catch sensitive data that’s inadvertently collected, they seemed to be “ineffective,” the lawmakers wrote.

The probe also found that Meta tools used by TaxAct allegedly collected even more information than previously reported, including the approximate amount of federal taxes a person owed. They said that Meta confirmed it used data collected from the tax software providers “to target ads to taxpayers, including for companies other than the tax prep companies themselves, and to train Meta’s own AI algorithms.”

The group believes that their findings indicate the tax prep companies “may have violated taxpayer privacy laws,” which could result in criminal penalties “up to $1,000 per instance and up to a year in prison,” according to the letter.

After calling for the agencies to investigate and prosecute where necessary, the lawmakers noted that new policies may mitigate the issue in the future.

“We also welcome the recent IRS announcement of a free, direct file pilot next year, which will give taxpayers the option to file taxes without sharing their data with untrustworthy and incompetent tax preparation firms,” they wrote.

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