Spanish public sector workers are striking against an average 5% cut in pay that comes into effect this month.
The cuts are part of a government austerity package aimed at reducing the budget deficit, after almost two years of recession.
Spain's government is under pressure from the European Union to slash spending but the trade unions say they are angry that public sector workers are being penalised.
Earlier, the EU said talks aimed at bringing member states' finances under control have progressed.
European finance ministers also started setting up the trillion dollar financial package agreed last month to defend the European single currency and stop the debt crisis in Greece from spreading.
Germany has also announced its biggest budget cut since World War II.
And the British government has warned of heavy spending cuts in its coming budget.