"We think quite a lot of people will follow the strike and this strike is not going to be the last protest," Juan Antonio Olmos, secretary general of the public sector union Comisiones Obreras (CCOO), said earlier.
A major protest march is scheduled later on Tuesday.
Spain's government aims to reduce its deficit by $19bn in 2010 and 2011, bringing the debt down from 11.2 per cent of gross domestic product in 2009 to 9.3 per cent in 2010 and 3 per cent in 2013.
Aside from wage cuts in the public sector, the measures will slash overseas aid, state investment, salaries for some senior government members, some tax-breaks for couples with babies, and automatic inflation-adjustments for pensions.
But unions have said that Jose Luis Rodriguez Zapatero's government should attempt to cut its deficit by raising revenue.
There are fears that Spain will fall into a similar situation to that of Greece, which in the face of a crippling debt crisis has been forced to take large bailout loans from the EU and International Monetary Fund (IMF).
Spain has an unemployment rate of more than 20 per cent, the highest in Europe.
The country emerged tentatively from recession in the first quarter of 2010 with growth of 0.1 per cent.