The party is hoping to block legislation which would make it easier for foreigners to obtain German citizenship and allow dual nationality.

CSU leader Theo Waigel has said all democratic means will be used to oppose the plans.

Mr Waigel, a former finance minister, was speaking before the opening of the annual congress of the party, which is the Bavarian ally of the main opposition Christian Democrats (CDU).

CSU spokesman Christian Schmidt: "There is a question of loyalty"

Earlier, Interior Minister Otto Schily strongly attacked the two parties, saying they were out of touch with reality.

"It's repulsive to claim that terror and extremism will be imported to Germany if we modernise our citizenship laws," Mr Schily said shortly before Mr Waigel's statement.

"It's defamatory to the foreigners who live here. It is a panic reaction to their loss of power," he added.

Gerhard Schröder's centre-left coalition of Social Democrats and Greens proposed the changes after it took power in the September 1998 election.

The two opposition parties have already announced plans for a massive petition against the laws - a move criticised by the Social Democrats, immigrant groups and Jewish organisations.

Blood ties

At present, German law recognises the principle of nationality by blood - for example, an ethnic German from Kazakhstan who has never lived in Germany can claim citizenship, but not a Turk born and raised in Germany and speaking only German.

Violent racist attacks have grown

The current law means about 9% of Germany's 82 million population is foreign. More than 60% of these people have lived in Germany for more than 10 years.

The reform would allow immigrants to hold a German passport without giving up citizenship of their mother countries.

Third-generation immigrants born in Germany would automatically become German citizens and foreigners who had lived in Germany for eight years could apply for naturalisation.

The two opposition parties say the changes would create resentment of foreigners and encourage crime. They say it could also make it easier for foreign criminal groups to operate from Germany.

The government has accused the opposition of promoting racism. It says the moves will help immigrants integrate into German society.