House Republicans are trying to "keep the public in the dark" by blocking a new rule that requires broadcasters to post political ad data online, according to the media reform group Free Press.

The Federal Communications Commission adopted a measure in April that requires broadcasters to provide information about political ad buys -- including advertising rates -- on the Internet. Previously, the rule only required the files to be available to the public. However, in almost all cases anyone who wanted access to them had to physically visit the stations.

A House Appropriations subcommittee approved the 2013 Financial Services bill on Wednesday, which includes a provision to block the new FCC rule. Democrats tried to strip the provision from the bill, but lost a party-line vote.

"Some members of Congress, working at the behest of the broadcast industry, want to keep the public in the dark," Free Press Action Fund Senior Policy Counsel Corie Wright said. "The FCC's online political file rules will shine a brighter light on the political ads that have inundated local airwaves this year."

"Broadcasters spent nearly $14 million on lobbyists in 2011," Wright added. "Now they’re spending millions more on campaign contributions to buy support from some members of Congress -- but that's a drop in the bucket compared to over $3 billion in political ad revenues that television stations stand to pull in this election cycle."

NBC News, ABC News, Fox News, The Washington Post, The Wall Street Journal, USA Today, Politico, The Atlanta Journal-Constitution have all lobbied against the measure.

"This information is already available in paper format, and it is entirely reasonable to make it accessible online, especially when there is little actual cost to doing so," Rep. Jose Serrano said.