U.S. small business confidence in May edged down after surging to a four-year high in a month earlier, signaling that the sector felt less upbeat about the economic outlook, a leading industry association reported Tuesday.

The National Federation of Independent Business (NFIB) said that its Small-Business Optimism Index decreased to 94.4 in May from April's 94.5, the highest level since December 2007.

Four of the ten index components dropped last month. The index gauging earning trends dropped three points to a net minus 15 percent, and the share of owners projecting higher sales dipped four points to a net two percent. It also implied most of small business owners had no plans to create jobs or enhance inventories.

The lack of progress is discouraging, producing no signs that economic activity will pick up this year at all, said the association, adding that the uncertainty on future economic policies would weigh heavy on small firms.

Some employment components, however, improved and profit trends remained stable relatively after its sharp gain in April, NFIB said.

The small business industry, accounting for 99 percent of the overall companies, is the major drive of the U.S. economy and holds half of American labor force.