In the early 80s lufthansas cabin crew union carried out radiation monitoring and when the preliminary measurements were announced management banned further monitoring.
It was fairly open knowledge in Swissair at the time as we had a lot of ex Luftwaffe pilots and one of our German Swiss skippers purchased his own measuring equipment which was one of the reasons that many of us cruised a few thousand feet below optimal FL.
IATA or IFALPA published a paper on it around that time and very quickly every copy was removed from our crew room.