If this is true and Bloomberg really had any b@lls, he would move to de-certify the union and have criminal racketeering charges brought against the union leadership. In an era of 10% unemployment the city could save a ton of money by hiring all new sanitation workers under a new collective bargaining agreement.
Of course, that would require Bloomberg to take the kind of action he only likes to take against smokers, trans-fats and legitimate gun dealers in other states.