Sabine Leutheusser-Schnarrenberger resigned after her fellow Free Democrats endorsed eavesdropping legislation favoured by the rest of Chancellor Helmut Kohl's three-party coalition. Her departure could unsettle the political balance which holds together the government.
The popularity of the Free Democrats, junior partners in Mr Kohl's government, has nosedived in the past year and party leaders hope adopting more conservative stands on some issues will help them survive.
In votes cast by about 35,000 Free Democrats, 63.3 per cent favoured letting law authorities plant eavesdropping bugs in suspected criminals' homes, said Guido Westerwelle, the party's general secretary. Ms Leutheusser- Schnarrenberger told reporters the proposed law is a threat to citizens' privacy. With tears in her eyes, she said the legislation "is a decisive step away from the concept of a liberal state of law" and her party's support for it "a change of direction in the domestic and law policies of the FDP".
Burkhard Hirsch, another Free Democrat, protested against his party's endorsement of the legislation by quitting as the party's spokesman on justice issues and as a member of a parliamentary justice committee.
Mr Kohl's coalition, which has a razor-thin majority in parliament, has been buffeted in weeks past by the plunging popularity of the Free Democrats. The party has been voted out of several state parliaments over the past year.
Mr Kohl faces the question of whether to replace Ms Leutheusser-Schnarrenberger with another Free Democrat or with someone from his own Christian Democrats or from the Christian Social Union, the other group in his coalition.Reuse content