I had this happen to me a while back as I was working while going to college. Admittedly, it was when the minimum wage was $5.00/hr and they raised it to $5.25 per hour so nothing drastic like $7.00/hr to $15.00/hr but for a college student it was a decent increase. The problem was, I was already making $5.25 per hour because I was good at my job and had earned a pay raise.
So, the week after the minimum wage increase went into effect my co-workers, who had not earned a raise, were now making $5.25 per hour and I was looking forward to my $5.50 per hour. Check came in, checked my totals, and my pay was $5.25 per hour. I explained to the store manager that this was incorrect and, at first, he just kinda laughed and said it was correct. I explained to him that no, it was not, because my pay was tied directly to the minimum wage and I had EARNED a pay raise of $0.25/hr and I asked him to explain to me how it was fair for the other three employees (small store) to be making the same I was when they had not earned a raise, but been handed one by the government. He just stood there for a minute with his mouth hanging open and said "You're right. Let me talk to corporate." Sure enough, our parent corporation agreed with me and increased my pay to where it should be and paid me my missing wages for the previous week.
Unless I am a salaried employee, I _always_ make it plain to my company that my pay is tied to the minimum wage and if it goes up my pay goes up by a corresponding amount -- otherwise, I just took a pay cut and someone fresh off the street without my years of experience with the company could be making nearly as much as I do (depending on the increase of the minimum wage vs. my wage, of course).