Whether you have a right of setoff against garnishments may be a matter of state law. For example, you can't exercise setoff in front of an IRS levy (which isn't a garnishment order under the regulation, anyhow), but you might be able to setoff in front of a state-court-issued garnishment order. Check with bank counsel to determine when setoffs may and may not be taken, and the technical requirements involving default, etc.
John S. Burnett
Fighting for Compliance since 1976
Bankers' Threads User #8