If posting already-public information on political ad spending is so damaging to broadcasters, as the National Association of Broadcasters argues, then why has one of the country's biggest cable providers been doing it since 2010?

Back then, Time Warner Cable created an online portal to search information regarding political ads sold on its system. Initially the portal served only the east coast, but has since provided data nationwide since 2011, according to a Time Warner spokesman. The ad buy records are available as downloadable PDFs.

Current law requires TV stations to keep political ad purchase orders on file at their stations — a rule that goes for broadcasters and cable networks alike.

Discovery of the portal comes during a fight being waged over an FCC rule that would require these records to be posted online. In April, the Federal Communications Commission passed a rule trying to get local over-the-air broadcasters to do just this. But the stations' association, the National Association of Broadcasters, has pushed back, even filing a lawsuit in May, saying that the order would be arbitrary because it does not force cable companies to do the same. Indeed, the rule would require online posting only by stations affiliated with the four major networks and only in the top 50 markets. (After two years, all broadcast stations will have to post the files online.)

So, if Time Warner isn't required to post the records online, why is it doing it anyway?

Because it's easier, cheaper and better, according to Alex Dudley, spokesman for Time Warner Cable. He said it makes complying with audits easier and reduces paperwork headaches.

“It’s less expensive because it’s digital,” Dudley explained. Furthermore, "You’re not running six weeks behind. Everyone’s seeing the information at once.”

Meanwhile, broadcasters have tried to block the rule, saying it would reveal sensitive ad rate information to advertisers and competitors. The FCC rebuffed this argument by pointing out that the information was already public, just not online.

And it's not only NAB that is trying to stop the rule. Last week, House Republicans tried to block the rule by defunding it.

The rule is still awaiting approval from the Office of Management and Budget. It could come into effect as early as next month, but might take longer if the OMB delays or has concerns. The NAB asked OMB to reject it this week.

We've sent an email to NAB asking for comment on Time Warner's portal and are awaiting a response. We will publish that as soon as we get it.

Free Press, a media reform group that has been pushing for the FCC rule for years (and with whom the Sunlight Foundation has been advocating for online access of the files), applauded Time Warner's portal.

"This points out what we've pointed out all along, which is this information is public and that putting this information online doesn't change the marketplace incentives," said Free Press attorney Corie Wright.

"If (Time Warner) thought it was so competititively sensitive, why would it do that?" she added.

Looking at the portal shows that American Crossroads, the super PAC brainchild of GOP operative Karl Rove, bought a two-week block of time in Portland, Maine, for nearly $3,000. The record shows when they aired on all cable networks–from CNN to Fox News to the History Channel. Fox News claimed the most expensive prime-time slot at $37 for a 30 second spot. A spot on CNN's American Morning cost $8 for 30 seconds.

Meanwhile, for about a month from early May to early June, the Obama campaign paid more than $6,000 to run ads on Portland’s Time Warner cable networks.

Some of the information goes back to the 2010 election. For example, records show ad time bought by Dan Maffei, a Syracuse-area Democrat who lost his Congressional seat that year and is now trying to win it back. Records also show what's coming: he has already bought time in September. 

The fact that Time Warner Cable puts this information online was pointed out by the Honolulu Civil Beat, which is published by eBay founder Pierre Omidyar, founder of the Omidyar Network, one of Sunlight's funders.

Meanwhile, so long as the rule remains in limbo, and given the fact that it will only apply to the nation's top 50 markets, Sunlight is asking for volunteers from the battleground state of Wisconsin to help track the files down.

6/15/2012, 6:10 p.m. ET: Updated to clarify that in two years, all broadcast stations would be required to post political ads online.