The Federal Reserve faces an unprecedented challenge as it prepares to set interest rates next week—making its decision with almost no economic data available.

The government shutdown has halted the release of most U.S. economic statistics, including the monthly jobs report. However, the Fed recently also lost access to one of its main private sources of backup data.

Payroll-processing giant ADP quietly stopped sharing its internal data with the central bank in late August, leaving Fed economists without a real-time measure that had covered about one-fifth of the nation’s private workforce. For years, the feed had served as a real-time check on job-market conditions between the Bureau of Labor Statistics’ monthly reports. Its sudden disappearance, first reported by The Wall Street Jou

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