This article, entitled California Union Blues: The Golden State’s unions fight to keep their members from controlling their own money, informs us about an issue that often gets limited public scrutiny:

The leadership of California’s largest public labor unions declared a crisis last week–and it had nothing to do with outsourcing, Enron, WorldCom, the minimum wage, healthcare, or any of the other causes that usually whip union bosses into frenzy. Instead, the controversy surrounds an initiative called “paycheck protection” which is now headed to Golden State voters in a special election this fall. The measure would require public sector unions to receive written permission from rank-and-file members before spending their dues on political activities.
While the issue doesn’t sound earth-shattering, the consequences for organized labor could be devastating…if the measure passes, union leaders will only have themselves to blame for supporting political candidates and positions that don’t square with a sizeable chunk of their membership.
In almost every election cycle, labor’s leadership takes millions of dollars in dues from rank and file members and ships it off to Democratic headquarters without asking…The system is highway robbery for union members who are forced to fund politics with which they don’t agree.
Exit polls and campaign finance data make the divide clear. For example, nationally, 38 percent of union members voted for George W. Bush in 2004. But according to the Center for Responsive Politics, 87 percent of all labor donations either went to John Kerry or other Democratic candidates. Republican presidential candidates aren’t alone…
The initiative which will go before the voters this fall only applies to public sector unions. Under current law, public sector union members have very few mechanisms to influence how their dues are used. While some unions technically allow members to get a refund of the portion of their dues that is spent on politics, doing so is complicated, cumbersome, and unadvertised…
Paycheck protection acts as an opt-in clause, forcing the leadership to get the written consent of union members before any of their money is spent on politics…
Of course the unions will not go quietly into the night. They defeated a similar measure in 1998 and are optimistic about their abilities to win political battles with the Governator, having sunk a Schwarzenegger plan earlier this year which would have moved state workers into 401(k)-style retirement plans…
The campaign’s biggest irony is that labor leaders are fighting the initiative by raising rank and file union dues. The California Teacher’s Association did exactly that recently, telling their membership that the dues increase will go to fight the paycheck protection provision. Their message: We want to take more of your money to make sure you won’t be able to control any of your money.
It’s a strange situation for union leaders to find themselves afraid of their own members.

It is indeed a strange situation. And yet another example of how unions raise cash to pursue their own political agenda, regardless of whether that agenda matches up with the beliefs of the people supplying the cash to the union’s coffers.
Here is another, relevant posting on the union dues issue entitled Learning More About How Dues Paid To Big Labor Are Spent. Here is another tangentially related posting on Union Pension Fund Politics.