This year all businesses with 50 or more employees must comply with the Affordable Care Act (ACA), offering qualified health care plans to workers, or face tax penalties. If a new survey of middle-market companies is any indication, that's going to cause a lot of confusion.

While 80 percent of midsize firm owners and executives said they were confident they met all other government workforce regulations such as payroll taxes, only one-third said they were extremely confident that they understood all of the new ACA regulations. The data comes from the 2015 mid-market survey by ADP, the payroll services company, released on Tuesday.

ADP polled owners and senior-level executives at 700 companies with between 50 and 999 employees, in September 2015. (Companies with 100 or more employees had to comply with the ACA starting in 2015.) Such companies are big job creators, responsible for hiring 48 million workers in the U.S., according to ADP.

Three-quarters of respondents said the potential for increased costs was their biggest concern related to the ACA, with one-third ranking health care costs stemming from the law as their top overall business concern.

The volume of government regulations was cited by 41 percent of survey respondents as their top business concern, which represents an 11 percentage point increase compared with 2014. More than a third of mid-market business owners and executives said they were hit with unexpected regulatory compliance costs in 2015. About half of those said they did not know how many fines they incurred, nor how much those fines cost their companies.