PARIS — All up and down the boulevard, store windows were smashed — at a Starbucks, a supermarket, a handbag store. Young men clambered on top of bus shelters. Even a children’s hospital was attacked. The police brought out tear gas and a rarely used water cannon.

Even for a country used to unruly labor protests, the violence on the streets of Paris on Tuesday was a shock. But days later, the man behind the antigovernment protests that have rippled across France was barely apologetic. If anything, he promised more.

Philippe Martinez, the mustachioed boss of one of France’s biggest labor unions, the General Confederation of Labor, known as C.G.T., has mobilized tens of thousands of workers and sent them coursing through the streets of French cities for weeks.

This past week, it was Paris’s turn. Mr. Martinez — 55, stocky, pugnacious and combative — ordered over 600 buses to ferry union protesters from the provinces to a march here, which drew tens of thousands of demonstrators on Tuesday.