I was once denied use of my boarding pass at JFK just prior to the WTMD (at a sort of boarding pass and ID check) and told to get my boarding pass reissued at the check-in counter. This was close to a decade ago, so I have to have my records checked to see which carrier was the operating carrier, which was the ticketing carrier, which was the marketing carrier, and which terminal it was at JFK -- it was a low number terminal IIRC. It was truly a bizarre situation compared to what else I've experienced in the US -- no less so because it had nothing to do with needing a visa or passport to travel. The boarding pass's scanability wasn't the issue.