A possible merger of General Motors Corp.'s (GM) European business and the Italian auto maker Fiat SpA (F.MI) could lead to a loss of up to 18,000 jobs, Klaus Franz, the head of the workers' council of German GM unit Adam Opel AG said Wednesday.

"I am critical regarding the merger," the top labor representative said Wednesday at a press conference following talks with Italian employee representatives.

The coming weeks will be "very important and decisive" for Adam Opel, he said.

Company Web site: www.opel.de; www.gm.com

-By Frankfurt Bureau, Dow Jones Newswires; +49 69 29725 500; katharina.becker@dowjones.com