Spain's unemployment rate soared to a new record of 27.2% of the workforce in the first quarter of 2013, according to official figures.
The total number of unemployed people in Spain has now passed the six million figure, although the rate of the increase has slowed.
The figures underline Spain's struggle to emerge from an economic crisis which began five years ago.
A big demonstration in Madrid is being planned against the austerity measures.
On Friday, Prime Minister Mariano Rajoy will unveil fiscal and policy measures aimed at halting recession in the eurozone's fourth-largest economy.
"These figures are worse than expected and highlight the serious situation of the Spanish economy as well as the shocking decoupling between the real and the financial economy," said Jose Luis Martinez, strategist at Citi.
Last week, the International Monetary Fund cut its 2013 forecast for Spain's growth to a 1.6% contraction from 1.5% and said the unemployment rate would peak at 27% this year.
The unemployment figure is the highest since at least 1976, the year after dictator Francisco Franco's death began Spain's transition to democracy.
The jobless rate, which stood at 7.9% in mid-2007, has risen relentlessly since the collapse in 2008 of a Spain's labour-intensive property boom.
On Wednesday, Mr Rajoy told parliament that the job situation for the entire year "will not be good, but it will be less bad than in the preceding years".
"Next year we will have growth and jobs will be created in our country," he said.
Meanwhile, in France, the second biggest eurozone economy, official figures to be released later on Thursday are also expected to show a record number of jobless workers.