Chancellor Angela Merkel on Monday reminded German carmakers that Brussels is in charge of negotiating the bloc's trade policy, a day before auto bosses are to hold talks at the White House as punishing US tariffs loom.
Merkel said the talks would focus on the companies' future plans as major employers in the US.
"Trade issues are unanimously decided by the European Commission for all member states," Merkel stressed at a press conference.
"But at the same time, German car manufacturers are large employers in the US and so there is reason for them to talk with the American administration about issues like which investments, which future they see," she added.
Pressed by reporters on whether German firms were bypassing Brussels, Merkel's spokesman Steffen Seibert was more outspoken, underscoring that there was "a clear line" to be drawn.
"The responsibility for trade policy lies with the European Commission, not national governments and certainly not car companies," Seibert said.
Volkswagen CEO Herbert Diess and Daimler boss Dieter Zetsche will take part in the Washington talks, according to DPA news agency, while BMW told AFP it was sending finance chief Nicolas Peter.
President Donald Trump has threatened to slap tariffs of up to 25 percent on cars imported into the US, a move that would badly hurt German automakers at a time when the Chinese market is already cooling because of a US-China trade row.
Trump and European Commission President Jean-Claude Juncker agreed in July to hold off from imposing new levies while negotiations were ongoing.
But as recently as last week the US leader indicated he was still in favour of using tariffs to protect the American auto industry.
EU Trade Commissioner Cecilia Malmstrom has warned that any US car duties would meet with immediate retaliation.
Trump has in the past repeatedly singled out German car brands in his criticism of the country's "very unfair" trade imbalance with the United States.
After he once complained that there were too many Mercedes in New York City, Germany's then economy minister retorted that Americans should "build better cars".