Over at Religion & Politics, Tiffany Stanley, who edits the online journal from the Danforth Center, has a report on "Pulpit Freedom Sunday." This is the day that a variety of pastors explicitly break the law which prohibits all 501 (c) 3s, including churches, from engaging in partisan endorsements. Full disclosure: I am on the advisory board at R &P.
I looked at the origins of the law barring partisanship in the pulpit late last year in one of my monthly analysis pieces for NCR. You can find it here.