Retired FBI agent Jeff Lanza explains the phrase.
"Going dark means that the FBI will have no way to look at those conversations, those key communications that may help prevent a crime from happening or investigate one that's already occurred," Lanza said.
So the FBI wants Congress to grant the authority to wiretap internet companies just as they do telephone companies and monitor internet services like instant messages, e-mail or social media in real time.
A lobbying group representing internet companies says the so-called wiretap mandate will be dead on arrival in Congress.
But Lanza maintains law enforcement needs new wiretap authority to intercept communications of suspected criminals who use online services instead of phones.
"If we don't get it, it's much more difficult to keep the public safe and investigate these crimes," Lanza said.
But isn't there the potential for great abuse?
"Absolutely," he said. "There's always the potential for abuse whenever you give law enforcement the power to invade our privacy."
But Lanza says investigators would only look at online messages with probable cause and a judge's order.
Civil liberties advocates are also fighting the proposal which would carry heavy fines for companies who don't co-operate.