Germany's opposition conservatives are determined to fight to the bitter end to prevent the first ever immigration bill from becoming law.

They have now turned their energies to appeal to Federal President Johannes Rau not to sign the bill. The bill requires the consent of the Federal President to become law.

President Rau (photo) has to take into account conflicting opinions expressed by constitutional experts before giving the go-ahead.

In a last desperate attempt, opposition conservatives have also threatened to drag the issue to the constitutional court in Karlsruhe.

Both opposition CDU (Christian Democratic Union) leader Angela Merkel and chancellor candidate Edmund Stoiber appealed to the President through newspaper interviews not to sign the bill.

At the same time the two have announced that they would make immigration a central plank of their election campaign for the upcoming elections in September.

On Friday the opposition parties of CDU and CSU (Christian Social Union) staged a walkout after the vote condemning it as "false" and "unconstitutional"

Bavarian Premier Edmund Stoiber (photo), Chancellor Schröder's conservative challenger in the September election told reporters after the vote, "I am very worried that the constitution has been so brazenly trampled upon to achieve an alleged political goal".

In an interview with the "Frankfurter Allgemeinen Sonntagszeitung", CDU chief Angela Merkel said, "If Rau does sign the bill, we're left with no choice but to take the bill to the Federal Constitutional Court to scrutinise its legal passage".

Fear of foreigners grabbing jobs

The legislation which would allow a limited number of skilled non-EU workers into the country is under fire from the Christian Democrats who say that the new laws would open up the labour market to foreign workers at a time when too many Germans are unemployed.

German unemployment stands at about 9 percent and has risen to 18 percent in the eastern part of the country.

But business leaders too are warning the opposition not to play the immigration card in the election campaign.

Michael Rogowski, President of the German Industry Association (BDI), welcomed the passing of the bill in the Bundesrat on Friday, saying it would help firms fill skills gaps in key sectors.

About 1.5 million professional post currently lie empty due to a shortage of domestic skills.

"I hope that the topic will no longer be the subject of an emotionalised election campaign", he said in a statement.

Immigration an emotional issue

But that's easier said than done.

The debate is a highly emotional topic in a country that for years has refused to see itself as a country of immigration.

In the face of conservative opposition, the bill has already been watered down and undergone several amendments.

It envisages restricting current asylum practices as well as obliging foreigners to integrate, which includes participating in language and citizenship courses.