The latest local immigration enforcement program from Immigrations and Customs Enforcement, Secure Communities, is billed by the federal government as a voluntary partnership between Washington and state and local governments. As part of the initiative, when a criminal is booked by a participating agency, his fingerprints are sent to a federal immigration database to see whether they're in the country illegally. If there's a match, ICE will determine whether to deport that person. Secure Communities is supposed to blanket every city, county and state by 2013.

But some cities are questioning just how "voluntary" this partnership is.

Some local officials have raised concerns that the program doesn't actually "remove the most dangerous criminal aliens from the United States," which is its stated goal. Rather, they argue, it targets immigrants who have committed minor offenses, or none at all.

Regardless of their reasons for wanting out, though, cities are finding that participating in the program is harder to avoid than they expected. From the Huffington Post:

In an August document titled "Setting the Record Straight," ICE seemed to deny that any ambiguity existed. For the first time, the agency vaguely outlined how a city or county could avoid joining. The document states that if a jurisdiction wants to opt out, various stakeholders will meet to "discuss any issues and come to a resolution, which may include...removing the jurisdiction from the deployment plan." To date, no city has successfully been able to do this. But San Francisco may be the first; this week, Sheriff Hennessey sent a letter to DHS officials reiterating the city's request to exit the program. And just yesterday, leaders from two other California counties followed suit. ICE officials are reportedly considering this appeal.

San Francisco could turn out to be a test case for whether this program is really a mandate or not.