A group of European Union countries led by France and Germany pledged Tuesday to start taxing the trading of shares and some derivatives by 2016, amid strong opposition by countries that are worried about the tax's economic impact and its legal grounding.

The group supporting the financial transactions tax presented its latest political agreement to a meeting of finance ministers, saying the tax should be enforced step by step. It would start with a levy on shares and some derivatives-which haven't yet been specified-by January 2016. A final proposal on the tax would be agreed on by the end of the year, the statement said.