June 17 (Reuters) - Weakness in tech shares pulled Wall Street lower at the open on Thursday after the Federal Reserve signaled it could start tapering its stimulus earlier than expected, piling pressure on a sector that is seen as vulnerable to higher interest rates. The Dow Jones Industrial Average (.DJI) fell 19.3 points, or 0.06%, at the open to 34014.38. The S&P 500 (.SPX) fell 3.3 points, or 0.08%, at the open to 4220.37, while the Nasdaq Composite (.IXIC) dropped 40.6 points, or 0.29%, to 13999.126 at the opening bell.