Warren and Sanders asked the Justice Department, Federal Trade Commission, Treasury Department, and the IRS to investigate whether TaxSlayer, H&R Block, and TaxAct violated taxpayer privacy laws by sharing sensitive user information with the two tech firms. Senators also released their own report Wednesday detailing the accusations, first raised by The Markup last November.

The report alleges that for years, tax preparation companies infused their products with Meta and Google tracking pixels that revealed identifying information -- like a user's full name, address, and date of birth.

The senators also suggest that some of the information provided, like the forms a user accessed, could be used to show "whether taxpayers were eligible for certain deductions or exemptions."

The senators claim that the companies did not receive user consent to share this information, which could violate laws banning tax preparers from sharing tax return information with third parties, especially since much of this data could be used for advertising purposes.