BRUSSELS — A hotly contested tax on financial trades took a big step forward on Tuesday when European Union finance ministers allowed a vanguard of member states to proceed with the plan.

The so-called Robin Hood tax would apply to trading in stocks, bonds and derivatives. Although the tax would probably be small — one-tenth of a percentage point or less on the value of a trade — it could earn billions of euros for struggling European governments.

Algirdas Semeta, the European commissioner in charge of tax policy, called the decision “a major milestone in tax history” and said the levy could be imposed starting next year. But deep concerns about how it would work could still lead to delays.

The European Commission, the bloc’s policy-making arm, still needs to draft the final legislation, and the 11 states in favor of the law will have to give their unanimous approval before it becomes law — two more than the minimum required for legislation to be drafted.