It’s the last thing Dollar General Corp. and Family Dollar Stores Inc. need right now: an extra $15 a week deducted from the wages of customers already living paycheck to paycheck.

Under the taxes-and-spending deal hammered out this month between the U.S. Congress and the Obama administration, Americans will pay two percent more in payroll taxes. For an average Dollar General customer earning $40,000 annually, that adds up to $800 per year. And that’s money they potentially would have spent at dollar stores, said Edward Kelly, an analyst at Credit Suisse in New York.