Their comparable sales results were also shy of those from big-box competitor Wal-Mart, which last week reported its most robust quarterly comparable sales gain in four years.
Shares of Dollar Tree, which grew its same-store sales 1.2 percent during the second quarter, fell nearly 10 percent on Thursday. Analysts had been expecting the retailer to report a same-store sales lift 2.4 percent, according to Thomson Reuters.
Shares of Dollar General plunged 17 percent, after it reported an 0.7 percent uptick in comparable sales. Wall Street had been expecting a 2.6 percent increase, according to Thomson Reuters.
"Retail food deflation and a reduction in both SNAP participation rates and benefit levels, coupled with unseasonably mild spring weather, proved to be stronger than expected headwinds to our business," Dollar General CEO Todd Vasos said in a statement, referring to new rules that limit the number of people who qualify for food stamp benefits. "The competitive environment also intensified in select regions of the country."
Wall Street had been feeling bullish about the health of the low-income consumer, who has benefited from lower fuel prices and job and wage gains. That sentiment grew last week, when Wal-Mart U.S. reported a robust 1.6 percent lift in its same-store sales and a seventh-straight quarter of increased foot traffic.
Bob Sasser, CEO of Dollar Tree, said cost increases related to rent and health care continue to weigh on its customer base.
"We still believe the consumer is under a lot of pressure," Sasser said.