SANTIAGO, Chile — Chile's largest labor union called a nationwide strike on Thursday to demand improved labor conditions and tax reform, but officials said only a small percentage of workers participated.

Small groups of hooded protesters set up flaming barricades ahead of the strike, blocking morning traffic. They also threw firebombs and torched a public transit bus in the capital Santiago. Police arrested 67 people, and six officers were injured in clashes with demonstrators.

The Central Union of Workers condemned the violence. Students and copper miners later joined thousands of workers in largely peaceful marches along the streets, chanting and waving banners. Organizers estimated the crowd in the Chilean capital on Thursday at about 150,000 people. City officials said the number was closer to 30,000.

Interior Minister Andres Chadwick reported that only 6.4 percent of all public workers, or about 10,000 out of 161,000, joined the strike.

"There are no reasons to call a strike, but there are legitimate rights to manifest discrepancies in a democracy," Chadwick said.

Chile has rapid economic growth and low unemployment. But the world's top copper producer is also plagued by vast income inequality and an expensive education system that many deem unfair.

Education and tax reform remain key issues ahead of the Nov. 17 presidential election.

Former President Michelle Bachelet, the frontrunner in the race, wants to finance an education overhaul that would slash tuition fees by raising corporate taxes from 20 to 25 percent over four years. Her rival, former Economy Minister Pablo Longueira, opposes free education for all, but has not dismissed the possibility of a tax reform.