Laws haven't changed, and they can't refuse it. I use USPS for shotguns, and always take a copy of the receiving FFL with me in case there are questions. I also put a copy inside the case or box just in case there is an issue during shipment. Based on my understanding, you don't have to disclose that it's a long gun to the USPS. You do have to declare a firearm shipped though a common carrier.
I've never had an issue. Ask for the postmaster next time.