WASHINGTON (Reuters) -U.S. small-business sentiment improved further in August amid expectations for higher sales, but worries about the quality of available labor lingered.

The National Federation of Independent Business said on Tuesday its Small Business Optimism Index increased 0.5 point to 100.8 last month. The share of business owners expecting higher sales rose six points to 12%.

The survey's uncertainty index dropped four points to 93, but stayed well above the historical average. 

"While owners have cited an improvement in overall business health, labor quality remained the top issue on Main Street," said NFIB Chief Economist Bill Dunkelberg. 

Economists say an immigration crackdown by President Donald Trump's administration has reduced the pool of workers, contributing to a stagnation in job growth. 

The NFIB said 32% of owners reported job openings they could not fill in August, noting that the last time unfilled job openings fell below 32% was in July 2020.

Worker shortages were acute in the construction sector, with nearly half of businesses reporting vacancies they could not fill. It said the overall share of businesses reporting labor quality as the single most important problem for their business remained at 21%.