MADISON, Wis. (AP) -- Supporters of recalling Republican Gov. Scott Walker are blanketing Wisconsin to start gathering more than half a million signatures to force an election next year.

Two potential Democratic candidates and other supporters on Tuesday marched from a recall office in downtown Madison past the state Capitol and to the state elections board office to file required paperwork for the effort.

Organizers first filed electronically shortly after midnight so the signature collection could start immediately. Tuesday's filing was the required signed document.

Former Dane County Executive Kathleen Falk says that organizers will collect the required 540,000 signatures. She and Mahlon Mitchell, president of the Wisconsin Professional Firefighters union, led the march on Tuesday. Both are considering running against Walker if there is a recall.