A minimum wage would stop companies indirectly sucking the 'welfare-tit', where their employees are forced to have welfare/food stamps in order to just survive. http://www.theguardian.com/commentisfree/2013/oct/30/mcdonal...
"Only 11.3% of workers who will gain from an increase in the federal minimum wage to $9.50 per hour live in poor households."
http://marginalrevolution.com/marginalrevolution/2014/01/how...
If they could raise prices to completely offset an increase in costs, they would have done that already, and have higher profits as a result. They may raise prices, but it will not be revenue-neutral of profit-neutral for them.
also, for me it is far more improtant to note that, if i may guess, >90% of companies paying most of their workers a minimum wage do not operate on zero profit.
• Researchers find small one-time price increases in the restaurant industry (of about 0.7 percent following a 10 percent minimum wage increase), but not in other industries.
from "University of California, Berkeley study: Who Would be Affected by an Increase in Seattle’s Minimum Wage?" which is one of the two pieces of research commissioned in the development of the Seattle ordinance.[1] The research explored empirical evidence provided by similar minimum-wage increase ordinances in other cities. (9 total, I believe, including San Francisco.)
[1] http://murray.seattle.gov/wp-content/uploads/2014/03/UC-Berk...
In any case, you should realize that this is a major increase in costs to restaurants, not just 1 or 2 percent.
The numbers I've seen for profit margins in restaurants range from 2 to about 3 percent. Since 1/3 of costs in restaurants come from labor, a 30% increase in labor costs will mean that restaurants will have a negative profit margin of around 7 or 8 percent after the new minimum wage goes into effect.
This means that eventually there will likely be less workers, higher prices for food, and less restaurants.