Every so often a lawsuit comes along that proves to be a watershed moment in the development of a technology. TV has had quite a few of these, such as the 1984 Supreme Court ruling that confirmed the legitimacy of the VCR. Now we might have the makings of another important case—one against a startup called Aereo that plans to retransmit broadcast TV online for a monthly fee.

The quick background: Aereo plans to make it possible for its subscribers to watch live or recorded sporting events and other over-the-air TV shows on their mobile devices. The company says it will do this by embedding small broadcast antennas in data centers that can then pipe the programming over the Internet to its customers, who will pay $12 a month. Aereo’s service is due to be launched March 14 in New York City and then expand to other markets. Its investors include Barry Diller, who built the Fox TV network and once ran Paramount Pictures.

Now Fox is Diller’s foe. It and several other broadcasting companies are suing to try to stop Aereo’s launch. As you might expect, they claim that Aereo has no right to send their broadcasts to its customers without a license. Aereo counters: actually, we do have that right, because anyone can put up an antenna to get better TV reception, and so what if the antennas in question happen to be tiny and in a data center rather than on the viewers’ roofs.

With that as its model and its legal defense, Aereo is reminiscent of another technology the broadcasting industry once fought: cable TV. That began as a way for people who lived far from TV transmission towers to get better reception. Early cable pioneers basically just put up big antennas and ran cable out to customers. The broadcasters squawked and got federal regulators to inhibit what the cable industry could do, but only for so long. It’s funny how things turn out: Now a company that was born slinging cable controls NBC.

You can’t blame the TV broadcasters for trying to stop Aereo. Every company in the TV business is trying to make sure innovation happens on its own terms. But that’s why television and the Internet are mixing awkwardly, and why it’s time for one of those clarifying court cases that helps establish the ground rules.