In a forest on the outskirts of Atlanta last March, hundreds of protesters had gathered once again to try to stop the construction of a new police and fire training center.

For Timothy Bilodeau, a 26-year-old who had flown in from Boston, the fight that began in 2021 had gained new urgency after state troopers killed a protester in a shootout in the forest weeks earlier that also wounded an officer.

On the day that Mr. Bilodeau headed in, there was another fiery confrontation. A crowd marched to the development site, where some protesters threw fireworks and Molotov cocktails, setting equipment ablaze. The police arrested nearly two dozen protesters, including Mr. Bilodeau.

As Mr. Bilodeau saw it, he was taking a principled stand against the destruction of the forest. But prosecutors had a darker take: They charged Mr. Bilodeau and 22 others with domestic terrorism.

In all, 42 people involved in the demonstrations against the training facility have been charged under Georgia’s domestic terrorism law, making for one of the largest cases of its kind in the country on a charge that is rarely prosecuted.

As several states have added or expanded laws related to terrorism, or are considering doing so, the case in Georgia is at the center of debate about the need for these measures, the dangers they pose and, more fundamentally, what constitutes terrorism. (One proposal in New York has suggested that blocking traffic, a tactic occasionally used in demonstrations, could be considered domestic terrorism.)