They don't get paid by their employer, correct. To cover costs, the union backing them will typically issue strike pay. But the project doesn't make any progre

They don't get paid by their employer, correct. To cover costs, the union backing them will typically issue strike pay. But the project doesn't make any progress until they're back to work, and labor costs may be higher after negotiation. That's why parent commenter was surprised that France - a country with strong labor unions that strike often - still has lower per-mile infrastructure costs than the United States.