The $9 per hour should be a starting wage. Then regular raises until you reach "top rate" after about two years and then minimal cost of living raises of a few cents an hour once a year after that. At least that is how it was several years ago. It really depends on the contract the union negotiated but supermarket pay has been on the decline the last couple of decades.

Union dues are about $5 a week so the first .25/hr raise covers that and every other raise is yours to keep.