It follows the arrest of a Swiss intelligence officer in Frankfurt last week on spying charges.
According to the German newspaper Süddeutsche Zeitung, the spy was trying to find information about how German tax authorities manage to buy data from Swiss sources.
Since 2010, the North Rhine-Westphalia (NRW) state has paid millions of euros for data CDs, which contained secret Swiss bank accounts in banks like UBS and Credit Suisse.
The spy, who is believed to be a former UBS banker, was arrested last Friday under allegations that he had been searching for data on tax evaders since 2012.
German authorities believe he placed a mole inside NRW’s finance ministry, who then gave the Swiss spy the names of tax investigators.
The Swiss Federal Intelligence Service (FIS) is believed to have run the operation, according to the report.
Norbert Walter-Borjans, NRW finance minister, told the Kölner Stadt-Anzeiger newspaper, "If Switzerland is serious about turning away from the dubious business transactions of its financial institutions, then these stories have to stop.
“We have to quickly arrive at some constructive cooperation against tax fraud, or else the highly questionable financial jugglers will end up having the last laugh."
After the spy’s arrest, Guy Parmelin, Swiss defence minister said, "Switzerland, and not only the banks, but also small and medium-sized companies, research institutes, and international organisations which have their headquarters here, are regularly suffering cyber attacks, spy attempts and efforts to recruit their staff."