Germany's opposition leader says Chancellor Angela Merkel's government must introduce a financial transaction tax to secure his center-left party's support for the European Union's fiscal treaty.
Merkel's center-right government needs opposition parties to secure a two-thirds majority in Parliament for the ratification of the EU treaty enshrining fiscal discipline.
Frank-Walter Steinmeier told Sunday paper Bild am Sonntag his party will only back the treaty "if there will be a clear Cabinet decision to tax financial markets."
Merkel backs such a tax in principle but has cautioned that it must be introduced Europe-wide to have real impact.
The opposition also demands that a set of measures promoting growth and job creation in Europe's ailing southern nations be added to the treaty.
Both sides will meet June 13 to forge an agreement.