The U.S. Nuclear Regulatory Commission has approved licenses for new nuclear reactors for the first time in more than three decades.

The NRC voted Thursday on a request by U.S. energy producer Southern Company to build two new reactors at its Vogtle plant in the southern state of Georgia.

The U.S. currently has 104 nuclear reactors that produce about 20 percent of the nation’s electricity.

The last time the NRC issued a construction license for a new reactor was 1978, a year before the partial meltdown at the Three Mile Island nuclear plant in Pennsylvania.

The economic downturn, high costs of nuclear power and low natural gas prices have also deterred applications for new reactors. And last year’s Fukushima nuclear disaster in Japan has increased scrutiny of the industry.

The $14 billion reactors are slated to begin operating as early as 2016 and 2017. Southern Company has already spent hundreds of millions of dollars preparing the site, which is home to two other reactors. The U.S. Energy Department has approved more than $8 billion in federal loan guarantees toward the project.

The two planned reactors were originally seen as part of what the industry once anticipated would be a nuclear renaissance.

A group of nine advocacy organizations is planning to file suit if the license is approved. The organizations accuse the commission of not adequately considering lessons from the Fukushima accident, when four reactors were damaged in Japan’s earthquake and tsunami.