[Mistymillar]

A dilemma, if you had a choice to use another company that would still be a risk to the actual workers as they will get paid less if the company has less work. I know your point is not that you want a rebate but around the fact the workers were not paid for a decision their boss probably made, I would probably tell them you are withholding a payment for the lack of service which you would not have been likely to do had they been fairer to their workers who still need to pay their rent and feed their children whatever the weather.