The US central bank has opened the door to an interest rate cut, in a shift in guidance that follows criticism by President Donald Trump.
The Federal Reserve left rates on hold, but said uncertainties about the economic outlook could force its hand.
According to the vote, one Fed policymaker advocated an immediate cut, something the president has called for.
Officials have in recent weeks acknowledged that the trade war with China is darkening the outlook.
The policy-setting Federal Open Market Committee (FOMC) kept the key rate in the 2.25-2.5% range, but said "uncertainties about this outlook have increased" and the Fed "will act as appropriate to sustain the expansion."
The closely-watched Fed statement included a marked shift in language. No longer did the central bank say it would remain "patient" in assessing economic data.
"In light of these uncertainties and muted inflation pressures, the Committee will closely monitor the implications of incoming information for the economic outlook and will act as appropriate to sustain the expansion, with a strong labour market and inflation near its symmetric 2% objective," the FOMC statement said.
James Bullard, president of the Fed's St Louis regional branch, voted for a cut of 25 basis points.