U.S. stock index futures pointed to a lower open on Wall Street on Wednesday after data showed employers chopped more than half a million jobs in May, signaling conditions remained tough.

U.S. employers cut more 532,000 jobs, according to the ADP Employer Services report, slightly worse than the median forecast of 520,000, according to a survey of economists by Reuters. The report dampened hopes the recession was not deteriorating as quickly as thought.

Data set to be released after the opening bell includes the ISM non-manufacturing business activity index, due at 10 a.m. EDT (1400 GMT), and monthly factory orders also due at 10 a.m.

The numbers are worse than expected, slightly worse, and that's probably related to the run-up that we've had. It's going to give people a reason to sell today, said Angel Mata, managing director of listed equity trading at Stifel Nicolaus Capital Markets in Baltimore.

Everyone continues to believe that unemployment is going to go above 10 percent. But if it gets much worse than this, that will probably give people another reason to sell.

S&P 500 futures fell 8 points and were below fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration on the contract. Dow Jones Industrial Average futures dropped 41 points, while Nasdaq 100 futures dipped 9.25 points.

Investors will also watch Federal Reserve Chairman Ben Bernanke at 10 a.m., when he is set to speak on current economic and financial conditions and the federal budget before Congress.

Aetna Inc shares slid 8.6 percent to $24.92 in premarket trade after the health insurer cut its 2009 forecast late Tuesday, citing higher projected medical costs for its commercial business serving employers and lower revenue from its Medicare plans for seniors.

Valero Energy Corp tumbled 11.8 percent to $19.75 after the largest U.S. refiner said Tuesday it would post a second-quarter loss due to weak market conditions and indefinitely delay two expansion projects.

Credit Suisse turned more cautious on equities, taking its weightings down to benchmark from overweight. The firm wrote it remained concerned about the economic backdrop and that a recent rise in bond yields had undermined their valuation.

U.S. stocks rose for a fourth straight day on Tuesday as an upbeat report on home sales bolstered hopes for an economic recovery as well as for shares in construction companies. But a selloff in financials on worries about the dilutive impact of recent stock offerings limited a broader advance.

Since reaching 12-year lows on March 9, the Dow is up 35.1 percent and the S&P has risen 41.7 percent.

(Additional reporting by Ryan Vlastelica; Reporting by Chuck Mikolajczak; editing by Jeffrey Benkoe)