Does the government need a search warrant to get information about your Twitter activity -- information like deleted tweets, other users you communicate with, and the list of IP addresses you used to connect to the service? Today we joined the ACLU, New York Civil Liberties Union (NYCLU) and Public Citizen in telling a New York appeals court that the answer to that question is yes.

Malcolm Harris was one of the 700 Occupy Wall Street protesters arrested in October 2011 on the Brooklyn Bridge. New York City prosecutors sent a broad subpoena to Twitter requesting three months worth of information on Harris. In a troubling ruling, a New York trial court found that Harris had no legal standing to challenge the subpoena because he didn't own this data, Twitter did. Beyond gutting Harris' legal ability to challenge the subpoena, the trial court's decision also undermined privacy by allowing the government warrantless access to the content of communications. This includes Harris' tweets, as well his location, which is ascertainable through the IP addresses Twitter records when a person logs into the service. IP addresses can then be used to link a person to a specific location.

Fortunately, Twitter intervened and challenged the subpoena itself, arguing that a search warrant was required to access Harris' information. Happy to see a company stand up for one of its users, we supported Twitter in an amicus brief (PDF), arguing that the court's opinion raised significant First and Fourth Amendment concerns. Unfortunately, the trial court was not moved and denied Twitter's motion to quash just as it had denied Harris' before.

Now the case is moving up to a New York appellate court. First, Harris' lawyer filed a writ of mandamus, urging the appeals court to order the trial court to quash the subpoena. Then Twitter filed an appeal before the same court, asking it to reverse the trial court's decision to authorize the subpoena. We're urging the court, again, to find that Harris has standing to challenge the government action, quash the subpoena, and require prosecutors to get a search warrant instead.

As more of our personal data -- where we go, who we interact with, and what we're talking about or reading -- ends up in the hands of third parties, it becomes all the more important for users to be able to advocate for their constitutional rights for themselves. Individuals have long been able to challenge government requests to third parties that implicate constitutional rights, and here, Harris' constitutional rights are certainly implicated. As we've successfully argued in other cases, the government needs a search warrant in order to obtain both content and location data. When it comes to location data, the Supreme Court's decision in United States v. Jones earlier this year made this even clearer, as the court ruled law enforcement needed a warrant to install a GPS device on a car.

Moreover, the First Amendment, which protects freedom of speech and association, is implicated here too. It demands the government prove not only an "overriding and compelling" need for this information, but also a substantial connection between the information it seeks and the investigation it is conducting. The government has utterly failed to meet this standard in Harris' case, as he is facing a minor disorderly conduct charge.

As the case continues through the appellate process, we hope the court recognizes what is at stake. The future of free speech and privacy on the Internet is being implicated in a case involving nothing more than a simple act of civil disobedience that typically gets dismissed at the initial court appearance. Instead, the court has a chance to allow users to challenge government overreach and reinforce how our longstanding constitutional rights apply in an increasingly digital world.