MADISON, Wis. (AP) -- Former U.S. Rep. Dave Obey says Wisconsin Democrats must unite against Republican Gov. Scott Walker and not form a "suicide pact" by attacking one another in the primary race.

Obey spoke Wednesday on a conference call arranged by Milwaukee Mayor Tom Barrett. Obey supports Barrett. His chief rival, Kathleen Falk, has been attacking Barrett more aggressively this week leading up to the May 8 primary.

Barrett has criticized Falk's plan for restoring collective bargaining.

Obey says the only way Democrats can make credible arguments to defeat Walker is to earn the trust of Democrats, independents and Republicans and avoid "petty sniping."

Falk says "the real suicide is if elected officials ignore the grassroots." Falk says she is talking about "important differences" between herself and Barrett.