The central bank is set to release a policy statement and update its forecasts for the economy and interest rates. Afterward, Chair Janet Yellen will hold a news conference.
For weeks, it had been expected the Fed would raise rates at its June meeting. That view was also encouraged by the minutes of its most recent meeting in April.
The minutes suggested that the Fed could increase the rate if hiring and economic growth strengthened and inflation showed signs of accelerating toward the Fed's 2 percent target rate.
But this month, the government announced that employers added just 38,000 jobs in May- the weakest gain in five years - and that job growth averaged only 116,000 the past three months, down from 230,000 for the 12 months ending in April.
"There is uncertainty about what the Fed might do, and that is confusing markets and adding to market instability," said David Jones, chief economist at DMJ Advisors.