Thirty-four percent of Spain's 16,682,861 employees earned the minimum wage of €645 a month spread over 14 payments, according to tax office statistics.
Among the young, the figure was much higher, with 86 percent of the 33,681 employees aged under 18 in Spain collecting the so-called SMI.
For the just over a million people aged 18 to 25 working in Spain last year, 74.7 percent earned the minimum salary, while in the 26–35 age bracket, the figure was 38 percent.
The tax office figures also show that almost half of Spain's total workforce — or some 7.7 million people — were so-called 'mileuristas', or people earning €1,000 a month or less.
The mean average salary in Spain in 2013, according to the tax office, was €18,505 a year or €1,342 a month, 1.4 percent lower than a year earlier.
In September, the OECD warned falling Spanish wages could hurt Spain's recovery by spurring on deflation and reducing consumer demand. The International Monetary Fund, however, has repeatedly pushed for Spain to lower wages.
Spain in December 2013 froze the country's minimum wage for 2014, a move criticized by unions who argued the purchasing power of the salary had gone down 5.5 per cent in four years.
The Spanish minimum wage is almost the same as the Greek figure of €683.76 and below that of Italy (€880) and France (€1,430 before tax).
Portugal, with €565.83, is the only country in Western Europe with a lower minimum wage.
Germany in July introduced a minimum wage of €8.50 an hour.