WASHINGTON -- The home stretch of the 2012 general election is set to be one of the most transparent in terms of public knowledge about political advertising buys. On Friday the Federal Communications Commission ruled to require television broadcasters to put online their file of political advertising buys for the first time.

The ruling, which was supported by the two Democratic commissioners and opposed by the Republican commissioner, requires the major broadcasters -- CBS, ABC, Fox, and NBC -- operating in the top 50 media markets to begin placing their file of political advertising buys online six months after the ruling is published. This would mean that at least some details of the record advertising spending expected for the 2012 election would be publicly disclosed online, making this information widely accessible for the first time.

Stations in smaller media markets and stations unaffiliated with the major broadcast networks will have until 2014 to begin disclosing their political files online. A political file includes the amount of the advertising buy, the time slot and the buyer's name.

Commissioners Julius Genachowski and Mignon Clyburn, who are Democrats, voted for the rule, while Republican Robert McDowell voted against it.

The new rule by the FCC is widely opposed by broadcasters, led by the National Association of Broadcasters, who had sought to keep their advertising pricing secret.

"NAB respectfully disagrees with today's FCC decision and we're disappointed that the Commission rejected compromise proposals proffered by broadcasters that would have brought greater transparency to political ad buying," said Dennis Wharton, NAB vice president of communication, in a statement.

The move amounts to a tectonic plate shift in the landscape as the 2012 election shapes up to be the most expensive in modern history. Third-party groups, who have been freed to raise and spend unlimited sums by court decisions, including the Supreme Court's Citizens United ruling, are expected to spend as much as $1 billion, nearly three times the amount shelled out during the 2008 election.

Previously the political file was publicly available only to those people who could physically visit a broadcast station and then pay a small sum to copy the files. The FCC will now host a centralized database about political ad buys that can be accessed by members of the public, but broadcasters will not be required to make the information searchable or downloadable.

The decision was hailed by Democratic lawmakers and campaign finance reform, pro-transparency and public interest groups.

"The American people have a right to know who is influencing their elections,” said Rep. Robert Brady (D-Penn.), the ranking member of the Committee on House Administration, in a statement. "This decision is a small, but critical, step in that direction. We must continue the fight to expand disclosure and restore faith in our electoral system."

"Today’s vote is a win for transparency, open access to information and the public," said Corie Wright, senior policy counsel for the media reform group Free Press, in a statement. "For over a decade, public interest groups have been asking the FCC to give people unfettered access to the information they already have a legal right to see."

Campaign Legal Center policy director Meredith McGehee called the rule "an important victory for transparency and accountability" but added, "It is unfortunate that in this year’s election, there will still be many markets that are expected to see massive advertising campaigns by outside groups where this information will remain difficult to access."

A representative of pro-transparency group the Sunlight Foundation echoed these concerns. "While we commend the FCC for addressing the need for political ad disclosure, the limiting of disclosure requirements to the top media markets, fails to create crucial transparency of who is behind the political ads bombarding Americans to influence their vote," said Gabriela Schneider, the group's communication director, in a statement.

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