The Secret Money blog is a joint project of the Center for Investigative Reporting and National Public Radio.

The nation’s most powerful labor unions are ratcheting up their efforts to elect Barack Obama with massive voter outreach campaigns.

The AFL-CIO labor federation announced a new assault on John McCain today, saying it will blanket battleground states with mail, phone calls and personal visits to sway swing voters in the Democratic direction.

A mailer (below) hammering McCain on his health care plan is going out to union voters in Colorado, Virginia, Michigan, Ohio, Pennsylvania, Wisconsin and Florida. The slogan on the back of the mailer says, “John McCain Isn’t For Us.”

Another million flyers will be distributed at workplaces. Volunteers aim to make more than 150,000 phone calls and visit homes throughout the Midwest.

Separately, the Service Employees International Union reported spending $500,000 on Sunday to canvass voters in support of Obama. Both SEIU and the AFL-CIO have said this year’s efforts will be their largest voter mobilization campaigns ever.

Meanwhile, the Los Angeles Times reports today on union payments in recent years to political firms and nonprofits with personal connections to the union’s leadership. We tracked SEIU’s current web of political influence and money here.