In their opening brief to the Supreme Court, broadcasters challenge the legality of Aereo but also say that a win for the start-up streaming service would be “deeply problematic” and force them to reconsider the quality and quantity of shows on free, over-the-air TV.

Their 65-page brief, filed on Monday, argues that Aereo’s streaming of broadcast signals violates the Copyright Act, as well as Congress’ intent when it was passed in 1976. The TV networks contend that Aereo’s system of dime-sized remote antennas, assigned to each subscriber, still is a public performance, and requires broadcast stations’ approval over the transmission of their signal.

“At bottom, Aereo’s arguments are irreconcilable not just with the transmit clause and Congress’ manifest intent in enacting it, but also with the basic philosophy that copyright protection embodies,” the brief states. “As this Court has had little trouble recognizing in recent years, the Copyright Act does not tolerate business models premised on the unauthorized exploitation of the copyrighted works of others. Aereo’s massive, for-profit scheme for exploiting Petitioners’ public-performance rights is no exception.”

Broadcasters’ say that Congress kept the public performance clause of the Copyright Act “purposefully broad and technology neutral” to account for changes in the marketplace.

In the brief, broadcasters contend that “although Congress recognized that people typically watch retransmitted television programming in the privacy of their own homes, it unquestionably intended ‘the public’ to include subscribers to a broadcast retransmission service. To that end, Congress provided that one is transmitting a performance ‘to the public’ regardless of whether ‘ the members of the public capable of receiving the performance … receive it in the same place or in separate places and at the same time or at different times.'”

They added, “It is simply not plausible that a Congress so determined to guard against both existing technical workarounds and the risk that new technology might render the statute obsolete would have viewed the use of thousands of little antennas as making any difference.”

Oral arguments are scheduled for April 22.

Broadcasters say that were Aereo allowed to continue, cable and satellite companies would race to develop their own broadcast streaming services without paying retransmission fees. And while Aereo has argued that a win for broadcasters would threaten the growth of an emerging marketplace for streaming services, broadcasters say the big difference is that services like Netflix and Amazon pay for the rights to stream content.

The networks even said that the implications for an Aereo victory are broader than their own business, saying that “what is at stake is the basic right of every copyright holder to determine if, when, and how to make its copyrighted work available to the public.”

Aereo suffered a setback last week when a federal judge in Utah ordered that the company shut down its operations in Salt Lake City and Denver pending Supreme Court review.

Aereo contends that its service amounts to a private performance, and is bolstered by legal victories in federal court in New York and Boston.

The case is American Broadcasting Companies vs. Aereo.