Supervisory boards at two big German carmakers are to hold emergency meetings later after they were accused of breaching EU cartel rules.
Volkswagen and Daimler have declined to comment on the allegations that they and other German car giants colluded to fix the price of diesel emissions treatment systems.
The claims first surfaced on Friday in a report by Der Spiegel magazine.
The issue is under investigation by EU and German anti-trust regulators.
Companies found to have infringed EU cartel rules are liable to pay fines of up to 10% of their global revenue.
Other firms under investigation are BMW, Porsche and Audi.