Confidence among small business owners fell slightly last month despite improvements in the overall economy, according to a report released Tuesday.

The National Federation of Independent Businesses small business optimism index dropped 0.3 points in December, to 88.0. While 10 percent of small business owners increased employment during the month, 22 percent reduced employment.

"Continued weak sales and threatening domestic policies from Washington, have left small business owners with little to be optimistic about in the coming year," said NFIB chief economist William Dunkelberg.

Along with weak sales, a lack of access to credit may have been partly to blame for low small business optimism. Small firms with capital outlays remained at their record low of 44 percent. A net 15 percent of firms reported that loans were harder to get in December than in their last attempt.

Policymakers have honed in small business credit in recent months as unemployment remains high despite an overall return to economic growth. The Obama administration has called for greater government support for small business loans in order to get small firms hiring again.