Wednesday, March 30, 2016
In the sentence "I work _____ a small company," you can use either at or for.
"At a small company" is the more common way to say this, but both prepositions are absolutely fine and have almost exactly the same meaning.
I think that "for a small company" puts slightly more emphasis on the fact that the speaker is an employee of a larger organization and not in control of it. But the difference is slight, and I'm not sure that all native speakers would agree with me.