Liechtenstein has opened a legal case against a former employee of LGT bank over the alleged theft of client data now being used in a German tax probe.
The tax investigation is the biggest in German history
Heinrich Kieber and others are being investigated for allegedly stealing data to pass on to foreign authorities.
Liechtenstein is also seeking legal cooperation from German authorities.
The UK's tax authority, the HMRC, has confirmed it also paid an informant for data regarding UK citizens who have accounts in tax haven Liechtenstein.
The Liechtenstein prosecutor has asked the prosecutors in the German cities of Bochum and Munich "to obtain relevant information about the precise identities of the informants".
Prosecutors in Bochum have been leading the tax probe.
Germany launched its tax inquiry after reportedly paying 5m euros in January 2006 for a list of wealthy Germans with money stashed away in the tiny Alpine principality with tight bank secrecy laws.
Berlin said on Monday that it would share information it had obtained with other countries.
Investigators in the US, Australia, Italy, France, Sweden, Canada, New Zealand, Spain and the Czech Republic are among other countries hunting for taxpayers hiding their money in Liechtenstein.
On Sunday the UK tax authorities said they had made the move in a bid to protect the UK against those trying to "deprive the UK of tax revenues to which it is entitled".
It has not revealed how much it paid for the information.
'Uncooperative tax haven'
Authorities in Liechtenstein have condemned the purchase of what it says is confidential bank data.
LGT Treuhand, part controlled by the principality's royal family, claims the list of 1,400 customer names are contained on DVDs that were copied by Mr Kieber in 2002.
The data concerns about 1,400 clients, with close to half resident in Germany, the bank said.
"The data material illegally disclosed to the German authorities is limited... to the client data stolen from LGT Treuhand in 2002," said the bank.
Liechtenstein's ruler - Crown Prince Alois - has also argued that Germany's investigation is illegal.
But German prosecutors say their investigation has so far netted 163 people and led to the recovery of more than 27m euros in tax revenue.
The Organisation for Economic Co-operation and Development lists Liechtenstein as one of only three states remaining on its blacklist of "uncooperative tax havens".