BERLIN, Nov 23 (Reuters) - Germany is working on a new law to force energy companies to shut down several more coal-fired power plants as it tries to reach ambitious climate goals, a document seen by Reuters showed on Sunday.

According to a draft legislation prepared by the economy ministry, energy companies will be asked to reduce carbon emissions by at least 22 million tonnes by 2020.

Some 50 facilities already registered for decommission will not count, however, meaning that a further eight coal-fired power stations may be closed down.

Europe’s biggest economy is aiming to reduce its greenhouse gas emissions by 40 percent by 2020 from 1990 levels, but its environment ministry has already warned the country risks missing the target by between 5 and 8 percentage points.

Although Germany has seen a boom in green energy, accounting for about 25 percent of overall power generation, environmentalists criticise the country for its continued dependence on coal-fired plants, which made up nearly half of power generation last year.

The latest reduction in carbon emissions, if put into effect, would be shared equally between Germany’s power companies, among them major energy firms RWE, E.ON and Vattenfall.

They would be allowed to determine, however, which of their plants to decommission. “With that they are granted a maximum of flexibility,” the document said.

Economy Minister Sigmar Gabriel is expected to meet senior executives from energy companies in Berlin on Monday to discuss the plans, industry sources said, adding that private-sector companies would be looking for compensation from the government if new rules forced them to close down plants.

A spokesperson from E.ON declined to comment.

The latest measure is part of a raft of new climate rules which Chancellor Angela Merkel’s cabinet is expected to decide on Dec. 3. The programme will also include steps to boost energy efficiency.

Merkel’s government wants renewables to make up between 40-45 percent of power generation by 2025 and 55-60 percent by 2035 - targets that experts say are ambitious for an industrialised country.

The European Union agreed last month a pledge to cut greenhouse gases by at least 40 percent in 2030. (Reporting by Markus Wacket and Michael Nienaber; Editing by Clelia Oziel)