While Democrat Hannah-Beth Jackson has wrapped up the endorsements and financial support of nearly every labor union in California, there's one that she has missed. And that one could potentially be big.

The California Correctional Peace Officers Association -- a.k.a. the prison guards' union -- last week endorsed Republican Tony Strickland. This is the group that has started a recall drive against Gov. Arnold Schwarzenegger, but it's doubtful that all the union's political resources will be devoted to that effort.

In fact, according to a study by the state Fair Political Practices Commission, the Correctional Peace Officers Association has been the fifth-leading source of independent expenditures in California political campaigns since 2001. Over that period, it has spent $3.5 million on independent expenditures involving 30 candidates, with an average expenditure of $114,087.

The union plays both sides, politically speaking, regularly endorsing both Democrats and Republicans. It typically likes to pick winners, so in a close race like the one in the 19th Senate District, it won't be surprising if the union jumps in to try to make sure its favored candidate is victorious.