South Africa-based Desert Wolf told the BBC it had secured the sale of 25 units to a mining company after showing off the tech at a trade show.
It is marketing the device as a "riot control copter" that can tackle crowds "without endangering the lives of security staff".
But the International Trade Union Confederation is horrified by the idea.
"This is a deeply disturbing and repugnant development and we are convinced that any reasonable government will move quickly to stop the deployment of advanced battlefield technology on workers or indeed the public involved in legitimate protests and demonstrations," said spokesman Tim Noonan.
He added that the ITUC would now try to identify which company had ordered the drones.
"We will be taking this up as a matter of urgency with the unions in the mining sector globally," he added.