Can you release content under a free Creative Commons license, then change your mind and take that material back?

That’s the question posed in a simmering battle between media giant AOL and a three-person startup called Pro Populi, which had the audacity last month to launch apps for Google Glass and the iPhone that use AOL’s CrunchBase database — a huge storehouse of basic information about people and companies in the tech industry. In theory, the apps are perfectly legal: Since its 2007 launch the CrunchBase database has been published continuously under the Creative Commons CC-BY attribution license, which permits any use — commercial or non-commercial — provided the owner receives credit. In practice, though, AOL is very angry.

AOL Assistant General Counsel Jeff Grossman on Friday emailed Pro Populi’s CEO Peter Berger, insisting that he cease using CrunchBase data in Pro Populi’s People+ app. The email followed an earlier meeting with CrunchBase president Matt Kaufman where AOL made the same demand, but phrased it more congenially.

“On the chance that you may have misinterpreted Matt’s willingness to discuss the matter with you last week, and our reference to this as a ‘request,’ let me make clear, in more formal language, that we demand that People+ immediately cease and desist from its current violation and infringement of AOL’s/TechCrunch’s proprietary rights and other rights to CrunchBase, by removing the CrunchBase content from your People+ product and by ceasing any other use of CrunchBase-provided content,” writes Grossman.

AOL acquired CrunchBase when it bought TechCrunch from blogging stalwart Michael Arrington in 2010. The dataset is drawn from TechCrunch’s own research and from submissions crowdsourced from the Silicon Valley startup community, venture capitalists and others. It contains information on some 187,000 companies, and it’s tapped by websites like The Startup Universe, an interactive guide to startups and funding, and an iOS calendar app called Sunrise.

So far, AOL isn’t challenging those uses of its data. But the People+ app is different: It uses a new database created by Pro Populi and seeded with a complete copy of the CrunchBase dataset. The startup hopes its database will grow as users contribute their own information. But for now, it’s nearly a CrunchBase clone.

“[Y]our company’s People+ product in essence has made wholesale use of CrunchBase content to simply replicate what CrunchBase does,” wrote Grossman in another letter to the startup. The app, Grossman adds, “duplicates what CrunchBase offers in order to compete directly with us.”

Berger says copying CrunchBase is allowed under the Creative Commons license and disputes AOL’s claim that the People+ is nothing more than a copycat.

“They are playing a double game,” he says. “They don’t like that we are presenting their data better than them. We are a mobile app. They are still a web app.”

By definition, content licensed under Creative Commons can’t be locked up again; the license grants “worldwide, royalty-free, non-exclusive” and “perpetual” authorization to use the content. So AOL could change the license in the future and lock down anything new added to the database, but the data that Pro Populi already copied under the CC license remains free.

But in an interesting wrinkle, AOL argues that the way in which Pro Populi acquired the content gives AOL veto power over its use, essentially mooting the Creative Commons license.

That’s because Pro Populi downloaded the database through the CrunchBase API, a digital interface that allows anyone access to the data. Buried in the terms-of-service for the CrunchBase API is this caveat: AOL “reserves the right to continually review and evaluate all uses of the API, including those that appear more competitive than complementary in nature.” And AOL “reserves the right in its sole discretion (for any reason or for no reason) and at anytime without notice to You to … terminate your rights” to use “any CrunchBase content.”

“We reserve the right to review how people are using our data,” Kaufman says. “If we find that it is something that replicates our service, then we have the right to ask not to use the data.”

Kaufman declined to comment on whether CrunchBase has demanded other developers to delete CrunchBase data.

Diane Peters, the Creative Commons general counsel, said companies have the right to adopt a use policy for an API, even if it’s feeding Creative Commons content. But no company can order somebody to remove Creative Commons material that is being displayed properly within the terms of the license, she said.

“As a matter of copyright, once you have it, you have it, and can do what you want with it,” Peters says.

Pro Populi says it is not removing the content from its app.

The Electronic Frontier Foundation, which is representing the startup, sent AOL a letter Monday saying “People+ has the right to continue using the material that People+ has gathered to date.”

Mitch Stolz, the EFF attorney on the case, wrote that the app maker is “prepared to defend its rights as a Creative Commons licensee” and “would prefer to resolve the issue amicably.”