Germany 's economics ministry Sunday said government plans to cap a rise in household electricity prices aren't far-reaching enough, signaling major obstacles within Chancellor Angela Merkel's own center-right coalition if the legislation is to become law before the general election.

Environment Minister Peter Altmaier last week announced plans to freeze subsidies to renewable-power producers at current levels until the end of 2014 and force industry players to pay a greater share of the bill for
Germany 's energy shift to renewable power.

But Economic Ministry spokesman Adrian Toschev told Dow Jones Sunday that Mr. Altmaier's plans don't go far enough.

"We welcome the fact that the environmental minister is reacting to our long-standing call to reform the existing subsidies for renewable energies," said Mr. Toschev. "However, there is still the need for a more fundamental reform which would control costs more effectively by relying on elements of a free-market economy."

The economics ministry, which is led by Free Democrats leader Philipp Roesler, will continue to "participate constructively" in the discussion about how to reform the system, the ministry spokesman said.

He declined to comment on a report in German weekly Der Spiegel, which said an internal study by the economics ministry is convinced Mr. Altmaier's plan will fail as it won't solve the underlying problem of the current system.

Mr. Altmaier, a senior ally of Ms. Merkel in the Christian Democratic party, told German Sunday newspaper Frankfurter Allgemeine Sonntagszeitung he's determined to push legislation through by Aug. 1, well before the upcoming national parliamentary elections.

Ms. Merkel's ruling center-right coalition is becoming increasingly concerned the costs of Germany's energy shift towards renewables will become a political issue in the elections and hurt Ms. Merkel's chances for another term in office.

In another sign that opposition to Mr. Altmaier's plan is mounting, the head of
Germany 's opposition Social Democrats told the Bild am Sonntag newspaper that the SPD also wants to reduce the burden on consumers but disagrees with how the government wants to achieve it.

"The government is dishonest about power prices," SPD party head Sigmar Gabriel told the Sunday paper. "It complains about the rising surcharge for renewable energy, but at the same time earns hundreds of millions of euros through the value-added tax," Mr. Gabriel said.

Gabriel said the SPD wants the government to pay back this extra income to consumers. "That will be our position when we enter negotiations with the government," Mr. Gabriel told the paper.