German manufacturers say the speculation will only serve to damage the already unsettled motoring industry.
Professor Bernd Gottschalk, president of the German Association of the Automotive Industry (VDA), said: 'The talk about an extra burden on motorists simply cannot be allowed if the latest delicate developments in Germany's automotive sector are not to suffocate before they get established.
'With the record prices at the petrol pumps, customers buying cars are already extremely unsettled in any case; and most of the blame for this lies with the 'eco-tax'.
He said it was of paramount importance that the government restores consumer confidence and suggested tax cuts, not increases, would achieve this.
In fact the top priority of a responsible economic and employment policy must now be to restore consumer confidence. This requires the prospect of tax relief, not of greater burdens. This is the only way to show consumers good prospects for the future again.
The VDA has called on the German government to spend a greater proportion of the motoring tax it receives every year - estimated at €50 billion - on modernising the country's roads. Gottschalk added: 'Politics can no longer milk and bleed road traffic on all sides. This has to be stopped if Germany wants to move away from the bottom of the European league table.'