The federal government is ramping up pressure on a leading digital-currency company to turn over a vast amount of its customer records as part of a tax-evasion probe, an effort that is raising privacy alarms.

The Internal Revenue Service is focusing on Coinbase Inc., a popular exchange and “wallet” service for bitcoin, which has surged in value over the past year as a kind of digital alternative to gold.

Some consumers use bitcoin as a potentially faster, cheaper and more secure way to shop and transfer funds online. Its growing adoption, and perceived anonymity, has made the IRS more concerned about people using digital currency to evade paying taxes.

Coinbase claims it has more than 6.2 million customers and has helped exchange more than $6 billion worth of digital currency across 33 countries.

After getting court approval, the IRS in December served a so-called John Doe summons to Coinbase that demanded transaction and user profile records and other information on all of the company’s U.S. customers from 2013 to 2015, a request covering hundreds of thousands or more account holders. The Justice Department, representing the IRS, petitioned a federal court this month for an order enforcing the summons.