The Federal Reserve will release a policy statement later Wednesday at the end of a two-day meeting.
The Dow Jones industrial average lost 86 points, or 0.5 per cent, to 17,765 as of 9:35 a.m. Eastern time.
The Standard & Poor's 500 fell six points, or 0.3 per cent, to 2,067. The Nasdaq composite lost 13 points, or 0.3 per cent, to 4,924.
Oracle rose 4 per cent after reporting that its software and cloud businesses gained strength in its fiscal third quarter.
Oil dropped $1.04 to $42.43 a barrel. Crude is trading at a six-year low.
Bond prices rose. The yield on the 10-year Treasury note fell to 2.02 per cent.