Though the proposal is on the June 30 agenda for a first reading in the Bundestag or parliament, Chancellor Gerhard Schroeder wants to hold a confidence vote the next day.
The assembly would then be dissolved, and the draft law promoting the filters would fall under the body's "principle of discontinuity."
Deliberations would come to an end. And the whole proposal would have to be re-introduced, whatever government comes into power following elections in September.
The federal cabinet approved a draft law on the diesel filters on May 11. It would create tax incentives for particulate filters for both new and used diesel cars. Filter subsidies are still being discussed in the upper house of parliament.
The state of Rhineland-Palatinate introduced its own proposal on May 27, which called only for diesel-filter retrofitting. The bill, along with the federal proposal, will be discussed within the upper house's finance committee on June 22.
That assembly backed the proposal of three other German states on May 27, which likewise sought tax incentives only for retrofitting and not for new diesel vehicles.
If there is no solution to the impasse, the clean-air policy of Environment Minister Juergen Trittin "will be nothing more than hot air," said Bernd Gottschalk, president of the German auto industry association (VDA).
Trittin maintains that the government has met its commitment by presenting a plan that was approved by the federal cabinet on May 11.