Many countries already monitor and censor the internet on a regular basis, forbidding access to numerous sites that they consider to be subversive. During recent unrest, the governments of both Iran and China effectively shut down the internet by taking control of or blocking servers. Combined with switching off of cell phone transmitters, the steps proved effective in isolating dissidents. Could it happen here? Undoubtedly. Once the laws are in place a terrorist incident or something that could be plausibly described in those terms would be all that is needed to have government officials issue the order to bring the internet to a halt.
Don't throw away that telephone modem card just yet.
Dial-up BBS systems might just come back into vogue!