Does shannon require both ground and air open at such times?
Yes-company rules.
I can bet that customers will be putting severe pressure on the IAA to have that changed. Can't argue on safety grounds since many more busy UK and European airports combine the Air / Ground position at times.
Can see a good case for the tower being a 1 ATCO and 1 ATSA position all day everyday.
What would the ATCO union position on that be?
Having 2 controllers for one position (the approach radar position) throughout the shift period but requiring 3+ controllers for what in reality is 1 ATCO position in the tower seems more than a little odd.
As an interested observer, I think that chosing Shannon Tower for this protest may have been a bit of an own goal as it could in fact show that the tower positions are over-staffed especially compared to UK airports with higher traffic levels!!
Regards,
DFC