Germany's semi-ban on smoking in bars is unconstitutional, senior judges ruled Wednesday, because tiny one-room taverns cannot set aside space for patrons who smoke.

Legislation passed by the 16 states in the past year allows taverns and restaurants to set aside smoking areas. Publicans who operate tiny bars, often in converted shops, challenged the law, saying it discriminated against premises which cannot be partitioned.

The Federal Constitutional Court in Karlsruhe, southern Germany, agreed, directing the states of Baden-Wuerttemberg and Berlin to amend their legislation by the end of next year.

Until it is altered, the overall ban is to remain in effect, but will not apply to one-room bars with less than 75 square metres of floor space.

Judges said an outright ban would be constitutional, but the exemptions in the legislation were discriminatory.

Chief justice Hans-Juergen Papier said legislators were entitled to "protect the public from dangers to health, and the legislature can consider passive smoking to be such a danger." But exemptions must benefit all taverns equally.

Each of Germany's states has slightly different rules about smoking on premises selling food and drink. Other states are expected to adjust the rules in the light of the court ruling.