As federal regulators hammer away at a plan to give consumers more choice in their cable boxes, lawmakers and even some of the Federal Communications Commission's own senior officials say one big issue will need to be addressed before the agency can pass any new rules weakening the cable industry's grip over the set-top box.

That issue, which cable and content companies have flagged as an objection before the FCC, has to do with the protection of copyright. That may sound boring, but it's what greases the wheels for billions of dollars in TV programming and economic activity every year, and it ultimately shapes what you get to see on your screen. But it's not just the cable companies that say the FCC's plan jeopardizes copyright. The nation's top copyright officials, too, have taken issue with it.

"My office has met with the Copyright Office, and I know that the Copyright Office has expressed concern about just what you described," Democratic FCC Commissioner Jessica Rosenworcel told House lawmakers Tuesday. "So I think more work is necessary on our part."

Rep. Marsha Blackburn (R-Tenn.) said Tuesday that she's heard from the Copyright Office, too, on the same issue. Another Democrat on the commission, Mignon Clyburn, said copyright protections "must be in place" in any final rule, but stopped short of saying the FCC's initial plan had problems.

But what, exactly, is the issue they're talking about?

Well, let's start with the FCC's proposal. The agency basically wants to decouple your cable TV content from the box you currently rent from your cable company for a monthly fee. In theory, that would mean any other company could take that content, repackage it, and put it in their own box — and then sell that box on the open market. This could potentially lead to more competition in an industry that's currently dominated by cable firms, which make hundreds of dollars a year from the average household from box rentals.

Cable industry critics of this proposal say it would open the door to tech companies inserting ads on top of the content they've taken from cable companies, thereby profiting from programming they technically didn't secure the rights to themselves. And, they say, it would effectively remove the anti-piracy protections built into today's cable boxes that keep thieves from making and distributing illegal copies of shows and movies.

"The proposed approach would circumvent the [cable company's] technological protection measures and license restrictions, with no enforceable means to prevent streaming that movie outside the home, in clear violation of the license to the [cable company], and the content owner’s copyright," industry officials argued last month in a regulatory filing.

The FCC's chairman, Tom Wheeler, has said advances in technology have made it easier to ensure that copyright is protected while still making life easier for consumers. But Wheeler also conceded Tuesday that he would work with the Copyright Office and others to make sure the final plan addresses those issues.

Some copyright lawyers who support the FCC's plan say the cable industry is simply "dressing" anticompetitive practices "in the rhetoric of copyright law," and that there's really no problem to speak of here.

"It’s hard as an initial matter to see what the Copyright Office could say" against the FCC plan, added John Bergmayer, a senior staff attorney at the consumer group Public Knowledge, "since giving users choice of what devices they use to access their [cable] subscriptions does not implicate any of the exclusive rights under the Copyright Act."

Still, the critiques from Republicans and Democrats, including from some of Wheeler's own Democratic colleagues on the commission, suggest the FCC plan may have to change if it is ultimately to pass, meaning the result could shift closer to the cable industry's position.

Cable officials have offered a counterproposal to the FCC plan, saying it allows consumers to get rid of their cable boxes while preserving copyright protections. The counteroffer would turn the set-top box into an app embedded in new smart TVs that can determine which content tier a cable customer has paid to see. And it would be adopted by all cable companies with more than 1 million subscribers. (It's worth noting here that Wheeler's plan, by comparison, would allow companies to design their own box-replacing apps, too.)

Wheeler has said he found the industry idea "heartening," but on Tuesday he took a shot at it, saying it was little more than a bit of calculated PR.

"One page is not a proposal," he said, "it's a press release."