Legal experts charged with advising German lawmakers have raised questions over the legality of plans for the European Central Bank to take over banking supervision powers next year, Der Spiegel reported.
The German weekly cited an analysis by the civil servants who work for the Bundestag Lower House of parliament as stating that European treaties suggest there is "no sufficiently sound legal basis" for the ECB's new role as banking overseer.
A move by European political leaders to centralize bank oversight under the ECB is the cornerstone of a planned banking union designed to strengthen the bloc's lenders against future financial crises.
But there has long been concern in Germany about a potential conflict of interest between the ECB's role as both supervisor and guardian of monetary policy.
The analysis was not yet available on the parliamentary website and the parliament was unavailable for comment.
European Union treaties state the ECB's remit is to ensure a stable currency and only in exceptional circumstances should it take over banking supervision duties, Der Spiegel wrote.
But the EU's plans suggested a "general transfer" of banking supervision duties to the ECB, which was "not covered by this warrant", the magazine continued, quoting the analysis.
A survey conducted by TNS-Emnid for the weekly Focus magazine showed 26 percent of Germans would consider backing a party that wanted to take Germany out of the euro and as many as four in 10 Germans in the 40-49 age bracket would do so.