Legally it isn't off-limits. Sanctuary is not a law, it's a tradition going back to the Old Testament. Not surprisingly, these churches harboring known criminals who have had their day in court and been accorded due process are ignoring the biblical history of this tradition, when it was for protection from vigilantes until the accused could have their day in court. 

The failure to enter churches to apprehend wanted individuals avoiding the consequences of their actions as determined by a judge is nothing more than a policy ICE follows as a political matter. I'm always fascinated by progressives who have no use or respect for religion or their organizations and fume at the lack of taxing them, allowing adherents to follow their faith, etc. Until it comes to the practice of harboring illegal aliens. Then churches are simply marvelous.