Aereo CEO Chet Kanojia.

The NFL and MLB are pushing for the Supreme Court to hear a challenge to Aereo, the service that allows viewers to stream privately broadcast television feeds online. In an amicus brief, the leagues argue that Aereo is designed solely to avoid paying copyright holders for retransmission fees. Those lost fees, they write, could force all copyright holders to move to paid cable networks like ESPN or TNT, "where Aereo-like services cannot hijack and exploit their programming without authorization."

"The revenues from these packages are an important source of income."

Moving to cable would be a major change for both leagues. CBS, NBC, and Fox currently broadcast 90 percent of the NFL's regular season games and all of its playoff games, including the Super Bowl. The MLB licenses around 400 games each year to broadcasters, including the World Series.

The leagues say that they've recognized the demand for streaming options, and that they've begun providing some, such as DirecTV's NFL Sunday Ticket. "The revenues from these packages are an important source of income that permits the leagues and their member clubs to provide the entertainment product that millions of fans worldwide are able to enjoy," they write. Though Aereo currently only allows its subscribers to stream from local stations — likely to avoid yet another heated legal challenge — the brief warns that Aereo could eventually remove that limitation, allowing it to effectively recreate subscription sports packages by bundling streams from different markets.

In their brief, the leagues frequently criticize Aereo's technology as well, referring to it as "gimmickry" meant to avoid copyrights. "[It] is neither technologically efficient nor innovative," the leagues write. It also points some blame toward the courts for Aereo's existence, writing that it operates through a "judicially created loophole."

TV networks have already petitioned the Supreme Court to hear the case, and while there's no certainty that it'll be taken up, it's clear that broadcasters want to determine Aereo's legality sooner rather than later. For its part, a major ruling in April by the United States Second Circuit Court of Appeals found that Aereo was not infringing on broadcasters' copyrights. Broadcasters have been threatening to leave the airwaves ever since, and we're likely to hear a lot more talk until they find an ultimate resolution.