FRANKFURT (Reuters) – German auto stocks took a hit in early Monday trading, weighed down by uncertainty over possible antitrust fines after European regulators said they were investigating allegations that carmakers were operating a cartel.

Shares in Volkswagen were down 3.3 percent, with premium rivals Daimler and BMW down 2.9 percent and 2.5 percent respectively, underperforming the blue-chip DAX index, which was 0.4 percent lower, and pushing down the Stoxx 600 index.

The car industry has been hit with billion-euro fines on both sides of the Atlantic in recent years for cartels related to various parts such as lighting systems, engine coolers and bearings.

The European Commission said on Saturday that European Union antitrust regulators had received a tip-off about another possible cartel.

Exane BNP Paribas automotive analyst Stuart Pearson said little was known about the allegations, and that no signs had emerged about price fixing towards the consumer. Allegations will, however, continue to weigh on stocks, he said.

“More ugly details could yet emerge, leaving German manufacturers – and the EU auto sector – still firmly in the sin bin for now,” Pearson said.

On Friday, German magazine Der Spiegel said VW, its Audi and Porsche brands and BMW may have colluded to fix the prices of diesel emissions treatment systems using industry committees.