With reference to the NBW link above:
Many volunteers "pay" for what they enjoy doing, and not just with their time, so the company complaing need to do a bit more research! Why shouldn't a charity get it's costs covered in providing them supervision and equipment?
Some examples of my own expenses:
I provide all my own recovery equipment as part of 4x4 Response Wales.
I bought my own specific radio for acting as a Safety Radio on car rallies, plus drive many miles each year to do it, and get no expenses.
Although St John provided a basic First Aid kit I purchased extra, more advanced equipment for my use.