BERLIN — German Chancellor Angela Merkel’s conservatives voiced reservations Friday about European Commission President Jean-Claude Juncker’s proposal to combine his post with the presidency of the European Council.

Michael Stübgen, an MP from Merkel’s Christian Democratic Union (CDU) who speaks for the party on European policy, said the proposal would “intervene massively in the institutional equilibrium of the EU.”

Juncker suggested the idea in his State of the Union speech to the European Parliament on Wednesday as part of a raft of proposals to drive forward EU integration. At the moment, the Commission president runs the EU’s executive body while the president of the Council coordinates among heads of state and government. But Jucker said that “Europe would be easier to understand if one captain was steering the ship.”

As the largest country in the EU, Germany will have a major say in whether many of Juncker’s proposals become reality. But Stübgen said detailed deliberations about his agenda would have to wait until after Germany’s general election, which takes place a week from Sunday.

“We will have to discuss his ideas one-by-one after the election,” he said.

With Merkel’s conservative bloc holding a big lead of about 15 percentage points over her key rival Martin Schulz’s Social Democrats, the longtime chancellor is cruising to a fourth term in office.

The key question of who will serve as her junior coalition partners, however, is unresolved. CDU officials in the Bundestag stress that this will have a substantial impact on the priorities and policies of the next government, including reforms to the EU proposed by Juncker.

The Social Democrats, Merkel’s current partners in government, gave a slightly warmer welcome to Juncker’s proposal — but stopped well short of endorsing the idea.

“Generally, Juncker’s proposal is to be welcomed, at least to have this discussion, regardless of whether it will actually lead to results or not,” Norbert Spinrath, a Social Democrat MP who is also the party spokesman on European policy, told POLITICO.

“Juncker wants to make clear with his proposals that the Council and the Commission aren’t automatically two different sides of the same coin.”

Merkel’s measured response

Juncker briefed Merkel ahead of his address about what he was going to say, German Finance Minister Wolfgang Schäuble told public broadcaster ARD Wednesday night, adding that the speech was “in line with our basic ideas for European policy.”

However, speaking to journalists on the sidelines of a meeting of EU finance ministers in Tallinn, Estonia on Friday, Schäuble expressed caution about all EU members joining the euro — another proposal in Juncker’s speech.

“For membership in the currency union, economic conditions need to be fulfilled,” Schäuble said. “As long as they are not fulfilled, it’s not in the interest of a country to become a member.”

Merkel herself struck a similar note on Friday after a meeting in Berlin with French Prime Minister Edouard Philippe.

“It’s already the case today that we strive for as many countries as possible to join the euro,” she said. “Any country that wants the euro and meets the criteria can join the euro.”

On Thursday, German Interior Thomas de Maizière also expressed skepticism about Juncker’s proposal to open up the travel-free Schengen area to all EU member countries.

He shared Juncker’s general vision for the EU, De Maizière said, “but, frankly speaking, there is still a long way to go.”