Long security lines snaked into baggage claim areas and parking garages at some U.S. airports this weekend, a possible indicator of more widespread travel problems as the latest government shutdown drags on.

That kind of disruption, while not yet widespread, is not a concern that typically surfaces at San Francisco International Airport, the largest of nearly two dozen U.S. airports where screening checkpoints are staffed by private contractors under a little-used federal program that allows airports to outsource security screenings while maintaining TSA oversight.

Because contractors’ pay comes from a federal contract, it often continues even when the government shuts down.