FRANKFURT (Reuters) – German carmaker Daimler (DAIGn.DE) defended industry committees on Friday, as cartel authorities examine allegations of collusion between BMW (BMWG.DE), Mercedes, Porsche, Audi and Volkswagen (VOWG_p.DE).

German magazine Der Spiegel reported last month that BMW, Mercedes, Porsche, Audi, and Volkswagen may have colluded to fix the prices of diesel emissions treatment systems using industry committees.

“Daimler is convinced that an exchange of opinions on technical issues between various manufacturers in the automotive industry is useful and that it accelerates many innovations or actually makes them possible,” the carmaker said in a statement to Reuters on Friday.

Der Spiegel said in its article that carmakers had agreed to limit the size of tanks for AdBlue, a filtering liquid used to remove nitrogen oxides from diesel emissions. The German carmakers had agreed to keep them small and had sought to standardize their size, the newspaper reported.

A survey of the biggest selling cars at Audi, BMW and Mercedes by Reuters shows that the vehicles do not have identically sized AdBlue tanks.

The AdBlue tank in the BMW 3 series has a capacity of 18 liters, while the Audi A4’s has 12 liters. Mercedes C-Class models can be fitted with tanks that are 25 liters or 8.5 liters in size. A variety of tank sizes is also evident in larger and smaller cars sold by BMW, Audi and Mercedes.

Daimler declined to comment on the allegations raised in the article, but said: “The Group takes note with concern of the discussions amongst the public and in the media and regards generalized prejudgments and dubious legal assessments as premature and damaging.”

Daimler said it had a certified antitrust compliance program, which fulfilled the highest requirements and was continually being further developed.

“Insofar as violations of antitrust law might have occurred, as a matter of principle Daimler cooperates openly and transparently with the responsible authorities,” Daimler added.

The European Commission said it had not started a formal anti-trust investigation against the carmakers, but that it was looking into the matter.

“The Commission and the Bundeskartellamt (German cartel office) have received information, which is currently being assessed under the leadership of the Commission as a matter of priority,” it said.

“It is premature to speculate on any potential competition concerns raised by the specific information received or on possible further steps.”