The San Diego Regional Chamber of Commerce’s measure of business optimism fell for the third consecutive month in September to another year-long low, with firms expressing concern about the impending state minimum wage hike and new aspects of the Affordable Care Act.

The chamber’s Business Outlook Index dropped slightly from 21.9 in August to 21.3. The index has historically averaged about 26. Its last major drop came last July when the city passed a minimum wage hike.

Businesses are worried about the state-mandated $10 minimum wage set to go into effect in January, along with upcoming ACA deadlines. Starting next year, small businesses with fewer than 100 workers will have to insure their full-time workforce. Small businesses with at least 100 employees will have to provide coverage for 95 percent of full-time workers, up from the current 70 percent threshold.

The chamber noted that about half of San Diego businesses surveyed said they didn’t know enough about the law to gauge how it would impact their bottom line, essentially the same proportion of companies without that knowledge two years ago.

Smaller firms were the least likely to feel informed about the law, while real estate and education-based companies struggled regardless of size, according to the survey.