I've heard anecdotal stories about my employer denying commissions to sales people when they end up being "too big".
Frankly I'm glad I'm not on a commission plan with them.
I think too many workers are afraid to file complaints against employers for fear of losing their jobs. I know I was.
My previous position, I got a % (as an annual bonus) of the bottom-line earnings of the office. Right before it was to be paid out, I was told that the office had to pay out a 4% "commission" to (coincidentally) the CEO/owner's daughter (who held my position prior to me obtaining it). This ended up lowering the office's profits and took about $2K out of my pocket.
The bottom line - I don't trust anyone. Big companies, small companies, unions, any of them. They're all out for their own good.