[Quanttek]

You can target the manufacturing plants since they are military objectives but you cannot target the workers. If any war-sustaining activity would make you, as a person, a target, pretty much anyone could be bombed: farmers, bankers, power plant engineers, truck drivers, ...

For a source, you can check out the Red Cross document I linked. Specifically, Ctrl+F for "continuous combat function" and read the commentary on recommendation V. The Guidance is considered authoritative in legal circles.