I know of a situation where a local organization rented out their hall to a local church, a legal entity and the people involved in the hall rental were all citizens/legal residents/documented aliens. The congregation is primarily Guatemalan, and it does a lot of ministry to the migrant farm workers in the area. The party was crashed by another group, who are well known to be iffy on documentation. The Church people attempted to deal with it themselves, but finally gave up and asked the hall owners to call the authorities.
They knew they were running the risk of some of their own people getting hit for being undocumented but they were of the attitude that the likes of those who crashed their party and tried to cause trouble give a bad name to those who are here properly and just trying to help their families.
I know all of this how, you ask? I was the person who made the call to the authorities.
Gabz, you did the right thing.