Not only do they sleep 'on the clock'; they sleep out in the open where everyone else can see them (including management). Some of the sleepy workers also have areas in these plants where they actually have cots or mats laid out to take a nap. (this is not a joke)
As a service technician, I was sent to a union plant to fix a malfunctioning piece of equipment. I was shocked on my first visit to learn that not only can I not touch the machine - there are "specialists" for each area of the machine. These "specialists" include electricians, pipe fitters, and millwrights (among others). So in order to remove a valve from a machine - you will need an electrician to disconnect the plug on the valve (1 screw), and a millwright to remove the valve (4 bolts). All of this will take 1-2 hours depending on if it's 'break time'. You cannot even open the electrical panel (a handle) because you are "doing the job of a union worker". Somehow this is an acceptable way of efficient buisness practice.
Another instance - A new machine needed to be disassembled outside of a union plant due to weight restrctions on the floor of the plant. Because our crew of four was 'taking the work of a union worker', there were 8 union employees who sat and watched us all week. These employees got paid $25-30/hr to sit outside and smoke cigarettes all day.