(4/27/12): This post has been updated.

The Federal Communications Commission voted 2-1 this morning to require broadcasters to post political ad data on the Web, making it easier for the public to see how as much as $3.2 billion will be spent on TV advertising in this election. 

The files, which detail the times ads aired, how much they cost and whether stations rejected ad buy requests from campaigns, among other things, are currently available only on paper at each station.

The FCC rejected an industry push to water down the measure. But the adopted rule also has serious limits. For example, the data will not be searchable or uploaded in a common format.

The rule will first apply to affiliates of the four major networks (ABC, CBS, NBC and Fox) in the top 50 TV markets. All other stations will have until July 2014 to comply.

“[L] arge areas of some swing states, like Virginia, Missouri, Wisconsin and Michigan, could see an influx of advertising in markets outside of the top 50,” the Sunlight Foundation noted in an analysis today.

(ProPublica has invited readers and other journalists around the country to retrieve the paper political ad files so we can post them online for all to see. We’ll continue to collect files from key markets not covered by the ruling. Sign up if you would like to contribute. )

Then there’s the crucial question of the format in which the files will be available. FCC spokeswoman Janice Wise told ProPublica that the commission is not creating a searchable database of the political ad files.

"We'll accept whatever [file] format they provide," she said in an email.

That will make it much more difficult to analyze the information.

Wise said there are no specific plans to make the database searchable.

By opting to allow stations to submit political data in any format, the commission departed from a recommendation made last year in an FCC working group report.  The report called for the political ad files to be put online and that “as much data as possible [be] in a standardized, machine-readable format” that “could also enhance the usefulness and accessibility of the data.”

Also unclear is how the broadcast industry, which vigorously lobbied against the rule, will react.

“[W]e will be seeking guidance from our Board of Directors regarding our options,” the National Association of Broadcasters said in a statement decrying the vote.

In March, the industry group submitted a supplemental statement to the commission raising “serious questions about the FCC’s authority” to require stations to put political ad data online.

“That was written as a legal memorandum, which is code for ‘we’ve lawyered up, and we’re ready to sue over this,’” says Andrew Schwartzman, a longtime FCC watcher at the Media Access Project.

The broadcasters’ group declined to comment beyond its statement.

On a Thursday earnings call for Belo Corp., one of the companies that has been fighting the disclosure measure, CEO Dunia Shive suggested that broadcasters would continue to fight the new disclosure rule.

“I don't think the conversation is over with respect to being able to continue talking about if we will ultimately have to include ad rates online," she said, Broadcasting & Cable reported.

Belo spokesman R. Paul Fry told ProPublica that the company merely “want[s] to continue the dialogue on this subject.”

The FCC also said today it would review the new rule after a year to see whether any changes need to be made before all stations are required to come into compliance in July 2014.

Wise, the FCC spokeswoman, said stations in the top 50 markets will have to start posting files 30 days after the Office of Management and Budget approves the rule. She said the FCC does not expect approval to take long.

In an analysis sent to clients and obtained by ProPublica, political ad tracking firm Kantar Media says the new rule will cover “about 60 percent of expected 2012 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.”

The 60 percent figure amounts to $1.8 billion out of an expected total of $3 billion in local spot TV spending.

Among the significant stations that will not have to post ad data this year: local CW and independent affiliates and Spanish-language TV like Univsion. (The Obama campaign has already released Spanish TV ads.)