New claims for US unemployment benefits rose unexpectedly, to 412,000 last week, an increase of 27,000 from the previous week.
That was above the 400,000 level which many economists believe signifies job growth.
The Labor Department said the jump in claims was thanks to a cyclical trend that is normal to see towards the end of a quarter, but markets were only partly consoled by that reading.
"Given the underlying downward trend we are inclined to see it as a one-time fluke, though we will be happier if we see a clear reversal next week," said Ian Shepherdson of High Frequency Economics.
Meanwhile, producer prices rose slightly less than expected in March, but still offered evidence that energy costs could trim growth.
In the first 30 minutes of trade, the Dow Jones Industrial Average fell 99.52 points (0.81 percent) at 12,171.92, while the broader S&P 500 fell 11.08 points (0.84 percent) at 1,303.33.
The tech-heavy Nasdaq Composite fell 25.21 points (0.91 percent) to 2,736.31.
Shares in Ford were hit by news the company will be forced to recall more than one million of its F-150 pick-up trucks. Ford was down 2.1 percent in early trade.
The bond market rose slightly. The yield on the 10-year Treasury fell to 3.45 percent, down from 3.47 percent on Wednesday. Meanwhile that on the 30-year bond stood at 4.54 percent, down from 4.55 percent.
Bond prices and yields move in opposite directions.