If a company has a "windfall" clause stating that when sales folks close large contracts (i.e higher than 50% of the quarterly target), that the company reserves the right to "limit" the commission on the sale, is there a case if they are not enforcing this consistently across the sales reps?

I have noticed that some sales reps are being hit with this and others are not, so does the company need to be consistent and if they aren;t being consistent, is there grounds for legal action?