Brokers at the German Stock Exchange in Frankfurt, Germany.

A plan to tax financial transactions in 11 European Union member states from 2014 is illegal, the bloc's lawyers have concluded, dealing what could be a final blow to the measure as proposed.

The findings are not binding but will make it harder to introduce a measure backed by Germany and others to make banks pay governments about 35 billion euros a year after receiving taxpayer aid during the 2007-09 financial crisis.