A battalion of union volunteers fanned out in North Philadelphia Saturday to knock on doors and fight a potential threat to Democrat Tom Wolf's campaign for governor: apathy.

The Service Employees International Union (SEIU) and PA Working Families organized the canvass, which put about 400 people on the streets to identify voters who support Wolf and to encourage them to come out to the polls Nov. 4.

Wolf has led Gov. Tom Corbett (R) by an average of 15 percentage points throughout the campaign, but Democratic strategists and their allies in the labor movement know that the party's base voters have proved more apt to turn out in presidential years than in a midterm election. The idea is to reach out and communicate with so-called "drop-off" voters.

"This election is not over yet," Wolf told the chanting, cheering crowd in the stifling basement of Miller Memorial Baptist Church on North 22nd Street. "If no one turns out, those polls don't mean anything," he said.

A series of speakers fired up the group by attacking Corbett for cuts to public education and tax policies they said favor corporations and the natural-gas industry.

"Pennsylvania is in the depths of a moral crisis – it's morally bankrupt," said Bishop Dwayne Royster, a leader of the Working Families group who heads the faith-based activist group POWER.

Corbett "decided it was more important to balance the books on the backs of our children than to ask the rich to pay their fair share," Royster said.

The canvassers included members of the Philadelphia Federation of Teachers, the Laborers and District 1199c of the health-care workers, as well as delegations from the activist groups Action United, Fight for Philly and MoveOn.

Their goal was to knock on 7,000 doors Saturday.