The European Union is poised to take its first formal steps to expand the world’s most ambitious limits on fossil fuel pollution. That may widen a rift in how it balances green policies with the need for cheaper power.

The 28-nation bloc’s regulatory arm is considering a proposal that would slash carbon emissions by 35 percent or 40 percent by 2030, deepening a target that expires in six years, according to a draft of the plan seen before its official release this week in Brussels.

The document will be the starting gun for a debate on the EU’s biggest change in energy policies in more than six years. It will pit countries such as Germany and the U.K. that want to step up efforts to protect the atmosphere against Poland and its allies, which are working to cap electricity costs that in some parts of the region are double U.S. levels.