Madrid (CNN) -- Tens of thousands of protesters converged on central Madrid Sunday as the so-called May 15 movement pushing for political and social change in Spain again took to the streets.
Madrid's was the first major demonstration of the day and drew some 37,000 people, Spain's state-run news agency reported, citing a consulting firm it hired to estimate the size of the crowd.
Protests were planned in 55 other Spanish cities later in the day and had gotten underway in Barcelona, Bilbao, Valencia and other cities, Spanish media reported.
The protests focused again on Spain's 21% unemployment rate and on the government's economic austerity measures. But on Sunday, they also rallied against European Union efforts to stabilize the euro, with many protesters worried that could lead to more austerity measures across the EU.
The movement takes its name from the opening round of large protests on May 15 of this year. On Sunday, it unveiled a new tactic in Madrid, when six columns of marchers started in the north, south, east and west of the capital. They walked noisily through neighborhoods, carrying banners and shouting slogans and quickly adding more protesters in a steady march to the Neptune plaza near the parliament building.
A throng of riot police stood by to protect the national parliament, days after violent scuffles occurred between demonstrators and police outside the Catalonia regional parliament in Barcelona last week.
"This capitalistic system doesn't work. It's an unfair system and a lot of people are in a very bad situation, without money," said Eva Fernandez, a social worker who was marching with the "northern" column down Madrid's main boulevard, la Castellana, on Sunday.
Protesters on June 12 dismantled a sprawling tent camp in Madrid's central Puerta del Sol plaza, nearly a month after it sparked large nationwide demonstrations and similar encampments in other cities to demand changes in Spain's political and economic system.
"The main thing we've achieved so far is to gain legitimacy to be able to protest and demonstrate in the streets," said Josua Serrano, a communications worker also marching in the "northern" column. "This civil disobedience is being practiced in a lot of countries now through nonviolent direct action. So people are going to the street without fear."
Before May 15, a series of citizens groups across Spain used social media networks like Facebook to call for protests on May 15. The large response seemed to surprise even the organizers, as tens of thousands of people turned out in Madrid, Barcelona and other cities.
The crowds have been dominated by young people, but also included retirees and families with young children. Demonstrators had a long and varied list of demands, but an underlying current was a call for change in Spain's political and economic system, to make it -- according to the protesters -- more democratic.
The movement gained force, with daily demonstrations involving thousands of people nationwide, in the run-up to May 22 municipal and regional elections. The conservative Popular Party was the big winner in that vote and now is poised, many analysts say, to win national parliamentary elections over the ruling Socialists. Those elections are expected no later than next March.
But the protesters have said repeatedly that neither of the two main parties represents their interests. Several protesters told CNN they voted for smaller parties which are farther left than the Socialists.
The protests of the May 15 movement have been largely peaceful, with police standing by. But there were scuffles, arrests and minor injuries at various flash points, including in Barcelona last week.