Spanish authorities have ordered the holders of about 3,000 secret bank accounts in Switzerland to pay tax on the undeclared funds by the end of the month, a newspaper has said.
The accounts, held by wealthy Spaniards, could hold a total of around 6.0 billion euros (7.4 billion dollars), the business daily Expansion said in its online edition.
Spain received details of the accounts from French authorities, the paper said, quoting "sources close to the case".
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It said the Spanish authorities have demanded the account holders pay tax, interest and fines on the undeclared amounts by June 30.
The report came as the Spanish government is pushing ahead with tough austerity measures to slash its massive public deficit.
Prime Minister Jose Luis Rodriguez Zapatero said last month that he plans a new tax on the richest people in the country.
But the government has ruled out declaring a "tax amnesty" to boost state coffers, as was approved in Italy this month and which allows repatriation of funds without explaining how they were earned.
Switzerland's neighbours and the world's leading economies have forced the country to offer concessions on banking secrecy over the past year, in an international clampdown on tax evasion.
The Swiss government has vowed to find ways to prevent foreigners from hiding undeclared funds in the country's banks.
