In the letter, EZ Lynk lawyers wrote that Apple and Google are planning to fight the subpoenas. Walmart declined to comment. None of the other companies subpoenaed responded to a comment request.

“These requests for potentially hundreds of thousands of people’s PII go well beyond the needs of this case and create serious privacy concerns,” wrote EZ Lynk’s lawyers in the letter. “Investigating this claim does not require identifying each person who has used the product.”

The government said in the letter its request for data was fair and appropriate, and it had “consistently sought customer information” because its lawyers want to interview witnesses about their use of EZ Lynk’s technology. It has already presented evidence to the court of people using the company’s tools to remove emissions controls on their cars, including Facebook and EZ Lynk forum posts outlining that use of the product.