Yes, but I'm sure you'd agree that isn't the point (whether it is true or not).
If you are a directly employed plumber, you are paid x under your contract to deliver y - loosely defined by what's in your job title - job description.
Are you on a bonus scheme linked to productivity? If you are, I can see why the warped thought-process could lead to this, but I don't see how this can be done without your agreement to it.
How does it have any impact on your money unless you are on a bonus scheme.
Go to the CAB by all means, but I think I know what I'm talking about here.