With Chicago hosting the NATO summit this weekend, protesters and police are braced for confrontation. Eight people have already been arrested for storming President Obama’s campaign headquarters. Others have pledged to “shut down” Boeing. And gas-mask sales have been brisk citywide. But much of the cat-and-mouse game will be technological, with people in the streets wielding smartphones to coordinate actions and publicize what’s happening, while law enforcement mulls whether to take the power of those phones away—disrupting service in the name of public safety.

While the tactic is usually associated with digital dictators abroad—and the Obama administration has sharply criticized such interruptions, even proposing sanctions against countries that curb their peoples’ wireless freedom—shutdowns are a creeping American phenomenon as well.

Often a perfectly legal one.

Not only do the FBI and Secret Service have standing authority to jam signals, but they along with state and local authorities can also push for the shutdown of cell towers, thanks to a little-known legacy of the Bush administration: “Standard Operating Procedure (SOP) 303," which lays out the nation’s official “Emergency Wireless Protocols.”

The protocols were developed after the 2005 London bombings in a process that calls to mind an M.C. Escher work. First, the National Security Telecommunications Advisory Committee (NSTAC) formed a task force— composed of anonymous government officials and executives from Cingular, Microsoft, Motorola, Sprint, and Verizon—that issued a private report to President Bush. Another acronym-dragging committee, also meeting in secret, then approved the task force’s recommendations. Thus, according to NSTAC’s 2006–07 annual issue review, SOP 303 was born.

"In time of national emergency," the review says, SOP 303 gives “State Homeland Security Advisors, their designees, or representatives of the DHS Homeland Security Operations Center” the power to call for “the termination of private wireless network connections… within an entire metropolitan area.” The decision is subject to review by the National Coordinating Center, a government-industry group responsible for the actual mechanics of the shutdown. The NCC is supposed to “authenticate” the shutdown via “a series of questions.” But SOP 303 does not specify, at least not publicly, what would constitute a “national emergency,” or what questions the NCC then asks “to determine if the shutdown is a necessary action.”

“It’s the nature of law enforcement to push the envelope… It’s act first and litigate second.”

So when would a shutdown occur? The precedents vary. In 2005, after the attacks on London, federal authorities turned off cellular network services in New York’s Lincoln, Holland, Queens, and Battery Park tunnels, fearing similar detonations, according to the review—which notes “that action was undertaken without prior notice to wireless carriers or the public.” In 2009, as President Obama was inaugurated, federal authorities used special equipment to jam signals in downtown Washington, citing the threat of remote-controlled bombs. Last summer, in response to the less catastrophic risk of a potentially violent protest following a police shooting, San Francisco transit officials shut off underground wireless service for three hours—a move the ACLU has said was the first and only known time a government agency in the U.S. has blocked electronic communications as a way to quell social unrest.

But there may already be other cases. Jamming is routinely used to secure visits from foreign dignitaries, according to a federal official who spoke to The Washington Post in 2009. Rumors of cellphone jamming also swirled around the Occupy protests in New York earlier this month; five people told The Daily Beast that they struggled to send photos, tweets, and basic text messages.

“It’s the nature of law enforcement to push the envelope,” said Eugene O’Donnell, a former New York City police instructor and professor of police practice at the John Jay College of Criminal Justice. “It’s act first and litigate second.”

While it’s against the law for individuals or nongovernmental organizations to sell or use jammers, the devices are easily found online. The U.S. military was among the first to use communications shutdowns, and local government demand for the technology has been building for years, even as the legal rules for its use have remained ill-defined. Prison wardens want to snuff out the use of smuggled cellphones by inmates; school officials hope to disable students’ phones; the National Transportation Safety Board wants to disable all “portable electronic devices within reach of the driver” while cars are in motion.

In Chicago, an alderman’s bill that would ban the practice was shunted off to committee. Questions about it compelled the mayor and police commissioner to say they had no plans to jam phones, but they didn’t take the option off the table.

Now other efforts to cut through the legal haze have emerged. In response to the wireless shutdown in San Francisco last summer, California State Sen. Alex Padilla introduced what would be a first-of-its-kind bill stipulating that to cut off service a judge must sign off that the move is necessary to avert “significant dangers to public health, safety or welfare.” If approved, the bill, which has the backing of the American Civil Liberties Union, could become the gold standard for state policy. San Francisco transit officials codified their own policy, which remains quite vague, after the public backlash to their shutdown. It calls for “strong evidence” of dangerous and unlawful activity, a belief that an interruption will “substantially reduce the likelihood of such an activity” and that the interruptions are “narrowly tailored.”

The Federal Communication Commission has launched the most ambitious effort, inviting a national conversation on guidelines. “We are concerned that there has been insufficient discussion, analysis and consideration of the questions raised by intentional interruptions of wireless service by government authorities,” the commission wrote in a request for public comments. In essence, it’s aiming to crowd-source a new version of the existing “Emergency Wireless Protocols” that would balance free speech, public safety, and security concerns.

But consensus is a long way off to judge by the public comments. Everyone seems to agree that government wireless shutdowns should be legal in certain circumstances, but defining those circumstances proves to be a vexing problem. So far there are only arguments, not answers about how to weigh free speech against security concerns. The head of BART calls shutdowns “a necessary tool to protect passengers.” Two law-enforcement organizations, the International Association of Chiefs of Police and the National Sheriffs' Association, urged the creation of a study group, suggesting SOP 303 as the standard to beat. Boeing asked the FCC to support the use of “wireless management devices” made by one of its subsidiaries, calling them a “nuanced, low-impact alternative” to widespread shutdowns.

The ACLU, Verizon, and a coalition of public-interest groups noted that cellphone blackouts would, with few exceptions, violate the Constitution and federal communication law, as well as threaten public safety by eliminating the means to share vital information or call 911. Individual respondents tended to agree, though a few offered particularly cranky dissents.

“Please do not in any manner, shape or form mistake the cell phone as a right or freedom,” wrote one commentator. “It appears our society is more concerned about liberties than being civil,” wrote another, who added, “I support the efforts of [San Francisco transit officials] and other agencies to quell these anarchist groups before their actions and mischief cause greater public harm than that of a simple wireless disruption."

Anarchists, and anyone else for that matter, have until May 30 to reply to these and other comments on the FCC website. The proceeding number is 12-52.