FRANKFURT (Reuters) – Germany’s carmakers VW, BMW, Audi, Porsche may have colluded to fix the prices of diesel emissions treatment systems using industry committees, German magazine Der Spiegel reported on Friday.

Germany’s cartel authority declined to comment on the report, which sent car stocks tumbling.

Volkswagen, Daimler and BMW shares were down 3.9 percent, 2.7 percent and 2.8 percent respectively, underperforming Germany’s blue-chip DAX index which was down 1.9 percent by 1401 GMT.

The Stoxx 600 autos index was down 3.1 percent.

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