A federal appeals court panel is skeptical whether streaming service Aereo has the right to retransmit broadcast television content without permission, but has yet to issue a decision. Three judges of the 2nd U.S. Circuit Court of Appeals appeared ready to reverse July’s lower court decision that reluctantly gave Aereo approval.

ABC, CBS, Fox and NBC are among the networks appealing the lower court judge’s decision that cited a Cablevision DVR case to allow Aereo to operate.

“Cablevision was a storage service, not a retransmission service,” says Bruce Keller, the networks’ attorney. “Aereo is a retransmission service by its own design. Without a license, it violates copyrights.” Paul Smith, another lawyer for the broadcasters, told the panel that the startup was trying to turn the Cablevision case “into a complete carte blanche where people can violate copyrights.”

Meanwhile, Aereo insists that it is complying with copyright laws and provides a legal, alternate platform for free TV broadcasts. Attorney R. David Hosp argued that Aereo lets customers “rent remotely located antennas to access content they could receive for free by installing the same equipment at home,” notes the Wall Street Journal.

“Aereo has grown from 100 users to more than 3,500 in the last year and has expanded from Apple devices such as the iPhone and iPad to devices including Windows computers,” reports WSJ. “It lets customers capture broadcasts from 29 local channels with subscriptions starting at $8 a month.”