Having been a branch secretary of the CPSA many moons ago I can say that then there were no payments made.
The only thing you could claim for was expenses where justified.
Your employer pays you normally for the time you spend on union activities during working hours - providing they agree that you can be released
For time spent on union duties outside your normal working hours - that's out of your community spirit and wish to help your colleagues - i.e. .. no money ..
The only folks who got paid a salary by a union were those directly employed by them.
I can't imagine it being any different now.