I don't really understand it myself. I realise there will be a new pay system with loads of new bands of salary. Not sure if this is correct but what I understand is that for some people, it will mean a loss of earnings and some will remain the same (for a while). Considering how university lecturers and other members of staff don't get much money, obviously they are not happy.
I understand they want to show their annoyance at the system but because I don't have any lectures/courses etc, the strike doesnt affect me at all. If I was on a taught programme, I will probably not be happy due to losing a day of lectures/teaching when I'm paying fees.