Seattle's elections watchdog says Facebook is violating a city law that requires the internet giant to reveal who pays for political advertising on its platform.

Wayne Barnett, executive director of the Seattle Ethics and Elections Commission, said in a statement Monday that Facebook failed to provide adequate detail about its advertisers' spending in city elections last year.

Facebook gave the elections commission a two-page spreadsheet that he said was insufficient documentation. The company said in a statement it had provided adequate details.

Barnett said he'll consult with prosecutors about how to proceed. He said Facebook could face fines of up to $5,000 per advertising buy.

He says Seattle and Washington law requires entities that accept political advertising to be transparent about the "exact nature and extent of the advertising services."