The number of U.S. workers who believe the economy is getting stronger fell by five percentage points in June to 24%, according to the index's survey.

"Workers are a bit more apprehensive about the state of economy given the market's reaction to the latest job reports, the Gulf Coast oil spill, as well as the European debt crisis," said SFN Group CEO Roy Krause. "Given all this, the job situation isn't as grim as it may seem. The number of temporary help services jobs has increased since last October -- this is a strong indicator of more employment growth to come. Within our own business, we are seeing a pick-up within the technology, mortgage services and administrative and clerical fields. In addition, we are also starting to see a rise in middle management searches within the finance and accounting field."

The index's survey questioned 1,252 employed adults in the U.S.