Union membership may be down, but politicians are still in the money. In the 2008 election cycle, labor unions spent:
Unions only cover 12.3 percent of workers today, but as this data from the Center for Responsive Politics shows, they still play a significant role in elections. They're a reliable source of cash for Democrats, who received 92 percent of union PAC money last election cycle. But it's important to note, however, that they are not even remotely close to the largest financial factor in electoral politics. Business interests spent $380 million over the same time frame. The comparison isn't perfect--individual firms have varying interests (though the same can be said of unions) and the money split almost evenly between Republicans and Democrats. But just as unions have some overarching common interests that guide the decision to support a particular candidate, so do most businesses. Unions spend a lot of money on elections, but they're not the only ones throwing cash around.