European Union (EU) plans to ban proprietary trading and break up the bloc's biggest banks are faltering as lawmakers clash over fundamental principles of the bill.

The European Commission, the EU's executive arm, presented its bank-structure overhaul a year ago to address the threat posed by too-big-to-fail banks. The bill has proven divisive in the European Parliament and among national governments, leading some legislators to say its days may be numbered.

"The chances of any serious progress on the proposal for structural reform of the banks are diminishing rapidly," Richard Reid, a research fellow for finance and regulation at the University of Dundee in Scotland, said by email. "In part it's because quite a few governments see no real need to substantially reshape their banking systems."