Columbia University law professor Tim Wu may have coined a phrase - "network neutrality" - that's become the cri de coeur for a generation of geeks and Internet evangelists. But maybe more than anyone, Wu knows it's a concept easier said than accomplished - or protected.

It might sound painfully wonkish, but bear with me. Net neutrality is essential if the Internet is to continue to live up to its tremendous promise. And it's once again at risk, thanks to some powerful companies and some wishful decisions by Congress, federal regulators, and the courts.

Net neutrality is the idea that Internet service providers - for most of us, major network owners such as Comcast, Verizon, and AT&T - should have to treat the data flowing on their lines or across their wireless networks, well, neutrally.

It's essential because everything we associate with the Internet and some things we probably forget to consider - from video to smartphone apps to e-mail to phone calls - flow as basic, binary data. Because the networks are mostly owned by companies whose legacy businesses are threatened by Internet-based innovators - Netflix and Vonage are two obvious examples - they have large incentives to discriminate in how the data bits are handled.

Wu has a long view of the challenges posed by companies that own network technologies. He proposed the idea of broadband "network neutrality" in a law-journal article a decade ago. More recently, he authored The Master Switch, a history of telecommunications that recounts 19th-century battles over the telegraph and telephone.

Whether or not Wu coined the phrase - he's not sure - he can't really lay claim to net neutrality itself. Before Congress and the courts got involved with broadband, the nation's phone networks always operated neutrally. For all Ma Bell's faults, she never listened into phone calls to give some priority over others.

I caught up with Wu on Wednesday to ask about the latest challenge to neutrality: a lawsuit by Verizon challenging the Federal Communications Commission's authority to impose even the modest neutrality rules it set in 2010, after the FCC's previous attempt was rejected by a federal appeals court.

Comcast, the nation's largest broadband company and the Philadelphia region's dominant provider, played a key role in that earlier challenge. Not this one. To win FCC approval of its acquisition of NBC Universal, it agreed to abide by the FCC's "Preserving the Open Internet" order for seven years.

Not so Verizon. A descendant of the Ma Bell monopoly and majority owner of the nation's largest mobile carrier, Verizon is a leading provider of both wire-line broadband and wireless Internet services.

As a network owner with a relatively small stake in content, Verizon plainly wants to capitalize on its multibillion-dollar investments. But Verizon's challenge makes a claim that could someday come to haunt everybody - and every business - that relies on Internet technology.

In its lawsuit against the FCC, which was filed with MetroPCS, a prepaid-wireless carrier, Verizon argues that the Constitution itself protects it from any FCC interference. It says the First Amendment gives it the right to exercise "editorial discretion" over the data traveling over its network, much like the owner of a newspaper is protected for decisions about which news articles and columns to publish.

Wu was so dismayed by Verizon's claims that he filed his own friend-of-the-court brief in the case pending before the U.S. Circuit Court of Appeals. He says that unless Verizon dramatically alters its business model - say, by only selling its selection of the "best 100 websites" - it is simply acting as a transmitter of data, not a publisher. If it prioritizes certain traffic, perhaps it's FedEx rather than the old Post Office. But it's still just a transmitter, he says.

Still, even if the courts reject Verizon's constitutional claims, as they should, that leaves the original problem, Wu says.

"We have to accept that these markets tend toward monopoly, and not pretend that they don't," he says.

Wu says government's key role should be doing "everything possible to prevent entrenching the monopoly" - to stop the dominant networks "from protecting themselves against disruptive innovation."

That's what every entrenched telecommunications monopoly has done before, Wu says, and this one is no different. Broadband is the telecommunications technology of the 21st century; we have to recognize it for what it is, even if that means tighter regulation.

If we want to reap broadband's benefits, Wu says, we can't let the network owners call all the shots.