Gary Becker, Nobel Laureate in economics, writes:
Unions always favor increases in minimum wages, even when as in this case the minimum only apply to some employers. Any increase in the minimum wage would raise the demand for unionized skilled workers who would substitute for the less skilled employees displaced by the minimum. Unions have an additional reason to try to raise the costs of big box companies like Wal-Mart’s since these companies do not have unions, and aggressively oppose them. Higher costs forced on non-union companies reduce the competition they offer to unionized companies.
The full post can be found here.