"This amendment would not hamper the government's ability to gather information regarding terrorists and spies, only its ability to spy on the rest of us in the process," the ACLU's letter reads.
A vote on Amash's amendment is expected on Wednesday and will reveal where lawmakers comes down on the surveillance programs that came to light last month. The White House and congressional leaders on the Intelligence Committees have been working to rally opposition to the amendment, saying it would curb a vital surveillance tool that's used to thwart terrorist attacks.
The NSA uses the authority under section 215 in the Patriot Act to operate the phone data collection program. The ACLU warns that the administration may be collecting other types of data about people under this section of the law.
They add that these records "are incredibly sensitive and reveal who we know, what we do, the faith we profess, our medical conditions, what we read and where we go."
The House will also consider another amendment from Rep. Richard Nugent (R-Fla.) that would prevent funding in the bill from being used by the NSA to obtain and store phone call and email data from U.S. citizens. The ACLU argues that this amendment "would reiterate current law" and doesn't prevent the NSA from "spying on Americans without cause."