Chicago's city council will vote today on a proposed minimum-wage law targeting "big box" retailers that marks a new stage in the political debate on the social impact of retailers such as Wal-Mart, Target and Home Depot.

While similar city minimum-wage laws exist in San Francisco, Albuquerque, Santa Fe and Washington DC, the Chicago law isthe first to be aimed onlyat retailers, covering those with annual sales of more than $1bn that operate stores with a floor spacein excess of 90,000 sq ft.