The mass demonstrations organized by 150 different groups included a march through the capital of Madrid that organizers said drew more than 72,000 people, thinkSpain reported.
Police put the figure at just 5,000.
Marches took place in other Spanish cities including eight provincial capitals. Demonstrations were also held in the Balearic and Canary Islands.
Many of the organizers called for a public vote on proposed government cutbacks revealed in newly released budgets.
Banners were displayed criticizing the cuts and accusing the government of Prime Minister Rajoy of leaving Spanish youth "with no future."
Union leaders said they believe the country's 2013 budgets will cause "greater recession and greater unemployment" than currently exists.
They also made renewed calls for a general strike.