The Federal Communications Commission has voted to require TV stations to post online the advertising rates they charge political candidates and advocacy groups.
Friday's vote came despite strong opposition from many broadcasters. They say posting advertising rates would undermine stations' competitive position in the marketplace and give advertisers unfair leverage over how much they are willing to pay.
Rate information is already publically available on paper at the stations.
The new rule will require stations to digitize and upload the information in real time to the FCC's website. Network-affiliated stations in the top 50 markets will have six months to comply. For all others, the deadline is 2014.
The FCC chairman says the information shouldn't be "stuck in a filing cabinet" in an online world.