[Sloth]

I wonder what authority FEMA would have over private security firms.

[aft_lizard]

The private security firms had to get there liscence to operate from some government.

[El Gato]

I wonder what authority FEMA would have over private security firms.

Same as they have over any private business or property. Since they were originally chartered to deal with the aftereffects of a nuclear war, they have pretty broad powers in their enabling legislation. Whether those powers are Constitutional has never been tested AFAIK, maybe they will be now.