Anybody who has ever used UPS knows that its employees work efficiently. UPS is the service-sector equivalent of the factory jobs that once created a blue collar middle class. But even if the low road is more profitable for UPS, the economy is broadly healthier with a large fraction of good, stable career jobs, if you factor in all the costs and benefits to society. There are really only two basic approaches. Since only ten percent of private sector workers belong to unions, the labor movement can't achieve this goal alone.
Most managers have a free hand to restructure work for industry's own benefit and convenience.
Government policy could deliberately remove some of the incentives to shift from fulltime to part time jobs. For example, all part time employees could be required to get the same hourly pay and fringe benefits as comparable full time ones. Temp agencies could be required to pay full health insurance and pension benefits. UPS maintained it had to cut costs by downgrading its jobs, because its competitors and customers are doing so. But that's precisely why society needs to rule out the low road for all of industry.