Union groups spent roughly $8.5 million helping the Democratic National Committee stage its convention in Denver four years ago, but most seem to be taking a pass this time around.

Labor leaders apparently are not pleased about this year's convention location, Charlotte, N.C. The state has been dubbed by some as the "least unionized" in the entire country, and there's not a single unionized hotel in all of Charlotte.

In July, AFL-CIO President Richard Trumka issued a memo noting, "This year we will not be making monetary contributions to the Convention or the Host Committee." Trumka also added that the organization would not be buying skyboxes or hosting any events, instead preferring to focus on a grassroots strategy in 2012. He listed voter registration as a top priority.

Though most prominent labor leaders say they continue to support President Obama and the Democrat Party as a whole, many of them decided to stage a "shadow convention" last weekend in Philadelphia. At the gathering, Trumka said the upcoming election "isn't about building one political party or hurting another," but rather about the long-term vision and goals of labor as a movement.

There is one key Obama ally from 2008 that is completely sitting this one out: the United Mine Workers of America. The organization primarily represents coal workers, and many have voiced their opposition to new government regulations they say are putting a stranglehold on the industry. Union officials say members have asked them to stay out of the race, so there are no plans to endorse any candidate.

The Romney-Ryan ticket seems to be itching to take up the union issue. Upon his return to his home state of Wisconsin, Rep. Paul Ryan quickly acknowledged the union-backed recall that Gov. Scott Walker survived.

"On June the 5th, courage was on the ballot in Wisconsin, and courage won," Ryan told the thousands of supporters gathered for his homecoming.

Earlier that day, Romney took a swipe at big labor unions while in North Carolina. "We put our kids and their parents and the teachers first - and the teacher's union, they'll have to go behind," he said.

The Republican National Committee seems willing to stoke the fire as well, having announced New Jersey Gov. Chris Christie as the keynote speaker for this year's convention in Tampa. He's repeatedly tangled with public employee unions in his state.