Unemployment is at a Eurozone high of 24.4 per cent, more than half of Spaniards under 25 years old are jobless, and Prime Minister Mariano Rajoy's conservative government has introduced stinging austerity measures in its first five months in office.
Speaking at a party rally, Rajoy, who on Friday announced a new set of tax hikes to come into effect next year, said he had "no alternative." He added, "Spain needs deep structural change, not makeup."
Protesters in northeastern Barcelona, northern Bilbao, eastern Valencia and many other regional capitals carried banners urging Rajoy to not "mess around with health and education."
Cayo Lara, lawmaker of the United Left party, said at a large gathering in Madrid that many protesters believed the government was intent on using the financial crisis as an excuse to sell off essential public services to the private sector.
Ruth Colomo, a 39-year-old teacher, said the country's public education system and national health service had been built up over decades with Spaniards' tax contributions.
"They are ours and I think we have the right to fight for them," she said.
Mechanic Evaristo Villar, 62, said he hoped Rajoy would listen to the protesters' concerns. "The government will hear us. I don't know, though, if it will pay any attention."