Police said about 58 people have been arrested and nine were slightly injured during face-offs on picket lines, but Interior Ministry officials said the work stoppage hasn't caused any major disruptions, The New York Times reported.
The strike called by Spain's two main trade unions protested an overhaul of labor rules that makes it less expensive for employers to hire and fire employees.
The walkout was called in advance of Prime Minister Mariano Rajoy's presenting Spain's 2012 budget, which is expected to include about $26 billion in spending cuts and tax increases to help the country reach its deficit targets as agreed with the European Commission.
Spain has about 23 percent of its workforce, or 5.3 million people, out of work.
Red Electrica, which operates the national electricity grid, said consumption was down 25 percent at 9 a.m., local time, Thursday, the Times reported. Most banks and retailers were open for business.
Although some flights were canceled, Madrid's airport was operating Thursday.
In Madrid, downtown streets had more traffic than usual because people used their cars to go to work and transit trains were operating on a reduced schedule, The Wall Street Journal reported.
A transportation association said protesters blocked highways in Catalonia and Valencia, and shut down industrial parks in Zaragoza, the Journal said.
Francisco Perez, a one-time union representative, told the Times the strike was a "useless response to the problems that Spain is facing."
"What is the point of a strike before even knowing what kind of budget this new government has put together and when unions have presented no alternative proposal to create jobs?" Perez asked.