The ACLU sued the DOJ over warrantless police surveillance.

The ACLU filed a Freedom of Information Act lawsuit to force the government to release statistics about its use of powerful electronic surveillance tools that law enforcement can use against any American simply by stating to a judge that it’s relevant to an investigation. The Department of Justice (DOJ) is required to disclose these statistics to Congress each year, yet routinely fails to do so. Today’s suit is an effort to compel the DOJ to follow the law.

The surveillance tools at issue are called pen registers and trap and trace devices. Originally these devices were designed to eavesdrop on the old analog telephone network, but now they refer to a broader type of electronic eavesdropping. Using these methods, the Justice Department has claimed the authority to reveal: 

• The phone numbers you call and that call you
• The time each call is made
• The length of each call
• The email addresses of the people you send emails to and who email you
• Your IP address and the IP addresses of computers you connect with (IP addresses can reveal physical location)
• The web addresses of the websites you visit

Without current data on the government’s use of warrantless and invasive searches into Americans’ private lives, we are once again left in the dark. This is a problem for two reasons. First, government transparency is of vital importance in a democracy. As the president emphasizes on the White House website, “Government should be transparent. Transparency promotes accountability and provides information for citizens about what their Government is doing.” The information we’re seeking is important because in order to have meaningful debate over government surveillance powers, we must be able to answer basic questions about the government’s current use of such powers.

But of more immediate concern, by subverting its legal obligation the DOJ has managed to completely escape the only oversight that Congress established on a very invasive surveillance power. Like a fire alarm, oversight mechanisms signal to Congress when the executive branch drastically expands its surveillance activities or oversteps the boundaries of its authority. Oversight also discourages executive agencies from taking such steps. Government overreach therefore becomes particularly worrisome when oversight mechanisms are not properly carried out.
http://www.aclu.org/blog/national-security/aclu-sues-doj-ignores-surveillance-transparency-law

ACLU Complaint: https://www.aclu.org/files/assets/2012_05_03_-_filed_complaint.pdf
ACLU FOIA request: https://www.aclu.org/files/assets/pen_register-trap_and_trace_foia_request.pdf