Commas

Q. We have a debate going on about the following sentence. Should there be a comma after the word states or not? Following rule 6.28 about commas before independent clauses joined by conjunctions, I believe it would. Thoughts? “The company operates in DC and all states except AK, ME, NH, NY, and RI.”

A. “Except AK, ME, etc.” is not actually an independent clause; it is a prepositional phrase. So there should be no comma after states.