Chancellor Angela Merkel's coalition was divided Wednesday over plans to allow the military to shoot down hijacked airliners in order to avert a Sept. 11-style attack.
Germany's supreme court last year rejected an air-safety law that would have allowed security forces to down a hijacked plane as a last resort.
Interior Minister Wolfgang Schaeuble on Wednesday gave the first public details of his plan B, an amendment to the constitution that would compare such a hijacking with a military attack.
However, a senior member of the Social Democratic Party, equal partner to Merkel's conservatives in Germany's coalition government, said the proposal would never pass parliament.
Sebastian Edathy, head of parliament's internal affairs committee, said it was wrong to put a hijacking on a par with defending the country against a conventional military assault.