MADISON, Wis. (AP) — A Democrat widely viewed as a union favorite emerged Wednesday to challenge Gov. Scott Walker, a day after petition circulators spurred by anger over the Republican's moves against organized labor said they submitted more than enough signatures to force a recall election.

Kathleen Falk's announcement was the first in a likely series of decisions by potential Democratic challengers to Walker now that recall petitions are in the hands of election officials. An influx of candidates would mean Democrats would have to hold a primary, pushing any election against Walker back another month.

Unions have been active in the recall campaign, which was driven by opposition to Walker's proposal passed last year that effectively ended collective bargaining rights for nearly all public sector workers. Having union support doesn't always translate directly into a win, however, and some rifts between union leaders and one potential Democratic candidate have already emerged.