Local TV stations will be required to post information including rates to a public database on the political ads they run, the Federal Communications Commission ruled Friday.

How will this work? The FCC will host an online database making available information about political ads running on local affiliates of the four major TV networks in the top 50 markets, according to the FCC. The database will be available 30 days after the Office of Management and Budget approves the new policy.

The files will include information on purchases of specific time slots.

"The new rule covers about 60 percent of all expected 2012 political advertising on local spot TV, where the vast majority of televised political ads air. The remaining 40 percent will occur in smaller media markets and thus remain offline this year, disclosed in the public files made available at stations," the Kantar Media Group's CMAG ad-tracking service wrote in an executive summary of today's ruling.

The information that will appear online is notoriously difficult to access. Local TV affiliates already make it publicly available, but only in paper copies at the stations themselves. For years, reporters and watchdog groups have had to travel to TV stations and examine records in person when seeking detailed information.

Broadcasters opposed the ruling, citing costs of disclosure and competition with other media forms. Television stations under federal law are required to offer political candidates the lowest available advertising rates.

"By forcing broadcasters to be the only medium to disclose on the Internet our political advertising rates, the FCC jeopardizes the competitive standing of stations that provide local news, entertainment, sports and life-saving weather information free of charge to tens of millions of Americans daily. We appreciate Commissioner McDowell's thoughtful and compelling dissent, and we will be seeking guidance from our Board of Directors regarding our options," the National Association of Broadcasters wrote in a statement responding to the ruling.

The FCC is made up of three commissioners, two of which were appointed by President Obama. Robert McDowell, the lone Republican appointee who was originally appointed by George W. Bush and reappointed by Obama in 2009, dissented from the decision.

Broadcasters will have to disclose the rates they charge for political ads, which are often lower than the rates charged to other advertisers. CMAG noted that this was a major reason broadcasters opposed the move.

"Although some in the industry have cited compliance costs, their real concern is that non-political advertisers will be able to look online and see the cheaper rates their political counterparts are paying-particularly the 'lowest unit rate' stations are required to charge candidates-and demand cheaper rates, themselves," CMAG wrote.

The watchdog group Citizens for Responsibility and Ethics in Washington had called for the online disclosure.

"With so much secret political spending by shadowy outside groups flooding our airwaves, it is more important than ever that we have some information regarding the identities of those who are trying to influence our votes," the group wrote in a blog post on Thursday. "Like so many things in Washington these days, the decision to make these allegedly publicly available documents online seems like a no brainer."

The FCC's move will give the public a far more granular picture of where and how political money is being spent.

Currently, it's very difficult to tell when and how political campaigns are spending money on advertisements. Outside groups-including super PACs and 501(c)4s-are subject to greater transparency. Those groups disclose ad spending to the FEC within 48 hours of purchasing air time, and the FEC reports it online almost immediately.

Campaigns, however, only disclose spending once a month-meaning that candidates themselves largely evade scrutiny on how much they're spending at any given time. By the time the public finds out, the data is already a month old.

With the FCC's ruling, that will change.