US retail sales declined by 0.3% in May compared with the previous month, amid falling petrol prices and lower demand for other goods.
The report showed the steepest monthly fall in retail spending since January 2016.
Online sales again surfaced as the strongest category, up 0.8% on the month and 10.2% compared with May 2016.
Analysts expect the US central bank to raise interest rates after its meeting today despite the weak report.
The estimates from the US Census Bureau showed retail spending rose 3.8% year-on-year.
Analysts had expected bigger monthly gains and the report weighed on US markets in morning trade.
The Dow Jones edged up 0.04% to 21,335.96, while the wider S&P 500 index fell 0.06% to 2,439.00,
The tech-heavy Nasdaq fell 0.04%, to 6,217.95.
Retail stocks were among the losers on Wednesday morning.
Sears Holdings, which announced layoffs earlier this week, was down about 2.2%, while Kohl's fell 2.5%. Macy's shares declined about 0.85%.