Coinbase’s CEO, Brian Armstrong, has estimated that it will cost the company between $100,000 and $1 million to defend its customers from what he described as an “overly broad subpoena.”

Last month, a federal judge in San Francisco ruled that Coinbase could be ordered, at the request of the Internal Revenue Service, to provide years of data that would reveal the identities of all its active United States-based users.

The IRS is concerned that some of Coinbase’s customers may have used its service to circumvent or mitigate tax liability. Federal investigators say they need Coinbase’s records to be able to identify some Bitcoin wallets and to check against tax records to make sure Coinbase’s users are paying any and all proper taxes on their Bitcoin-related income.

Coinbase, for its part, feels that it should not be compelled to do the government’s bidding on such a vast scale.

In a post on Medium that he published on Saturday, Armstrong also said that the company was doing its best to stay within the confines of the law. He noted: “We have worked to comply with all IRS guidance in our space, beginning with the March 2014 guidance on virtual currency.”

As Armstrong continued:

Other digital currency exchanges operating abroad (while still serving US customers) are unlikely to demonstrate a similar commitment to working with the IRS, yet we were the only company (as far as I know) to receive a subpoena for all customer records. I believe this is one of those situations that could have been resolved with a phone call instead of a subpoena, given our amicable interactions with the IRS in the past. My hope is that we can move toward that type of relationship in the future.

Coinbase has formally asked to intervene in the court proceedings and will make its first formal appearance before the judge on February 19, 2017.