In an effort to rein in overreaching law enforcement practices, Rep. Jason Chaffetz (R-Utah) and Sen. Ron Wyden (D-Ore.) yesterday re-introduced the GPS Act, which would require a warrant for location tracking and create a critical check on the growing use of these invasive searches.

While location tracking has become an increasingly common tool for law enforcement, proper regulation of this powerful technology has never been established. Police often track individuals' movements for days, weeks, and even months, often without a judge determining whether the surveillance is justified based upon a legitimate suspicion of criminal activity.

The ACLU does not oppose law enforcement embracing new technologies; however, safeguards must be put in place to protect our longstanding privacy rights from persistent, invasive surveillance. On January 23, 2012, the Supreme Court ruled in US v. Jones that that location tracking by law enforcement implicates the Fourth Amendment of the Constitution, and called on Congress to act to regulate GPS technology tracking. Justice Sonia Sotomayor explained how sensitive the data gathered from location tracking searches can be:

GPS monitoring generates a precise, comprehensive record of a person's public movements that reflects a wealth of detail about her familial, political, professional, religious, and sexual associations. … Awareness that the Government may be watching chills associational and expressive freedoms. And the Government's unrestrained power to assemble data that reveal private aspects of identity is susceptible to abuse.

As the ACLU's Catherine Crump testified before Congress last year, without limits on what the government can collect or how long it can keep what it collects, the government can store these records and data-mine the information for years into the future. Judicial oversight for location tracking, through a warrant requirement, would prevent law enforcement from conducting suspicionless surveillance solely at its discretion and would thereby protect the rights of all Americans.

Before the explosion of tracking technology in recent years, law enforcement needed to invest extensive time and resources to gather such detailed information, which created a natural deterrent against the practice. Today, given the ubiquity of cell phone towers and the increasing precision of cell site info, an officer can often just contact your cell phone provider to get specifics on where you have been or even attach a tracking device to your car – both without a warrant.

Law enforcement's location tracking policies should be clear, uniform and protective of privacy nationwide. Instead, they diverge widely, with agencies in different towns following different rules. In response to a recent ACLU FOIA request, the Department of Justice refused to disclose its policies on tracking citizens. Congress should step in and set a clear and protective standard across the board.

The danger unregulated location tracking poses to Americans' privacy is real, immediate and universal. We applaud Sen. Wyden and Rep. Chaffetz for introducing legislation to restore proper checks and balances to protect innocent Americans from unwarranted and invasive location tracking. The GPS Act, combined with the introduction of the ECPA Amendments Act this week, demonstrates that a bipartisan coalition is solidifying around guaranteeing our digital due process rights in 21st century America.

Learn more about the GPS Act and other civil liberty issues: Sign up for breaking news alerts, follow us on Twitter, and like us on Facebook.