Union workers may be an endangered species.

They now account for only 12 percent of the workforce, down from about 20 percent three decades ago, according to recently released estimates from the U.S. Department of Labor. Nationally, unions represented nearly 16.3 million workers last year, a 1 percent decline from 2015.

States with the lowest union representation continue to be concentrated in the South and places with right-to-work laws, which allow employees to opt out of paying union dues. Organized labor is least prevalent in Georgia, Louisiana, North Carolina and South Carolina, where fewer than 5 percent of workers are represented by unions.

SOURCE: BLS, 2016 annual averages

Union representation have been slowly declining for years, but the drop has been much more noticeable in some states.

In South Carolina, an estimated 52,000 workers were represented by unions last year, which is about 40 percent less than just three years ago. Alabama, Alaska, Oklahoma and Wisconsin also all recorded declines exceeding 20 percent since 2013. In nearly half (21) of states, unions represent less than one in 10 workers.

The gradual decline of unions carries many potential ramifications for states’ economies.

In general, union workers tend to earn higher wages than their nonunionized peers. According to the Labor Department, without controlling for different occupations or other factors, nonunion workers make only 80 percent of union members' median weekly earnings.

Not all states are following the same downward trend, though.

In the South, Mississippi's union employees have doubled over the past two years. More recently, workers at a major Nissan assembly plant there are attempting to unionize. Colorado, Delaware and Utah also recorded sizable upticks in union representation last year, although their numbers were fairly low to begin with.

If there's one major union stronghold left, it's the public sector. Nationwide union representation for government workers is five times that of the private sector -- but it too has dropped in recent years.

According to the latest estimates, 32.8 percent of state government employees are represented by unions, compared to 35 percent five years ago. Local-level employment, which includes large numbers of public safety and school employees, similarly decreased from a rate of 46.6 percent to 43.9 percent of the workforce over the five-year period.

NOTE: Numbers referenced in this story include a small number of workers who are not union members but are represented by unions.

State Union Representation Rates