Is the U.S. government allowed to gain control (thru conservatorship) of any private/publically-traded companies?

“Effectively, the federal government has now become the nation’s mortgage lender.”

I haven’t yet seen any citation of where in law/Constitution this kind of power is provided. There also doesn’t seem to be a great deal of opposition to the move (i.e. both presidential candidates are in favor of the takeover).

Anyway, I’m interested to know more. Is there historical precedent? Could, for example, the U.S. Government take over Microsoft should their software prove critical to the “safety of the nation”?