A proposed new bill in the U.S. Senate would give the president's office potent new powers over Intenet access in times declared as "cyberspace emergencies." Bill S.773 would grant the president authority to disconnect any privately-owned network from the Internet, at the president's discretion. You can read an excerpt of the bill here. 

The emergency powers clause is only a small part of Bill S.773 -- in its entirety, the bill is an effort to begin to improve the U.S government's fortification of the 'cyberspace' assets and infrastructure in the United States.

Many experts in network security have publicly stated that the U.S government was lagging behind other countries' grasp of the new world of information warfare. As key elements of infrastructure and communication are now controlled by computer networks, increasingly, in the 21st century the Internet will be seen as another potential battleground -- someday, perhaps one as important as the sea, the sky, or over land.

In particular, Russia and China are generally believed to have spent more time and money coordinating offense and defense assets to be deployed online, in comparison with the U.S and Europe. For example, about this time last year, Russia began a massive Internet disruption campaign against Georgia and Estonia, shutting down many government-run websites; while in Canada, researchers discovered a massive Chinese-run spy-ring, dubbed the 'Ghostnet', which had access to 1295 computers across 103 countries around the world. 

But as in the case with many Bills granting emergency powers, critics of the new legislation worry that some of the wording is too vague and ambiguous -- which could lead to abuse, where the government shuts down networks needlessly, without sufficient cause. "The designation of what is a critical infrastructure system or network as far as I can tell has no specific process. There's no provision for any administrative process or review. That's where the problems seem to start," Lee Tien, an attorney with the Electronic Frontier Foundation, was quoted as saying.