A landmark German immigration law enabling employers to seek labour abroad is poised to become a vicious battleground in the country's upcoming elections.

President Johannes Rau signed the bill into law after a three-month wrangle between the ruling Social Democrats, who proposed the legislation, and the conservative Christian Democrat Union (CDU), its bitter opponents.

CDU deputies walked out of parliament when the bill was passed in March, declaring that it had been forced through the house in a wholly unconstitutional manner.

President Rau criticised both parties for failing to find a compromise

Following President Rau's decision that parliament had followed protocol, the party announced its intention to take the issue to the country's highest tribunal, the Constitutional Court.

If this fails, the conservatives' candidate for chancellor, Edmund Stoiber, has vowed to abolish the law if he comes to power after September's general elections.

Economic needs

The law will allow a limited number of skilled workers into Germany to fill professional jobs that currently lie vacant - a move welcomed by many business leaders.

The conservatives have made much of Germany's high unemployment rate

It is the first law of its kind since the country stopped the "guest worker" programme under which immigrants, mainly of Turkish origin, were invited to the country to fill the jobs Germans did not want to do.

Now, while the German unemployment rate doggedly hovers at the four million mark, there are an estimated 1.5 million professional positions that cannot be filled owing to a skills shortage.

If employers are not able to look abroad to fill these places, the government argues, there will be serious consequences for the economy in the longer term.

Conservative caution

The bill makes no provision for unskilled workers, and will tighten asylum procedures. It will also oblige those foreigners who are in Germany to integrate.

Chancellor Gerhard Schroeder has been keen to stress that he is no liberal when it comes to immigration.

"Anyone who tries to block this bill is doing nothing to limit immigration," he said after the CDU and its partner, Mr Stoiber's Christian Social Union, announced it would contest the law.

The alliance argues that the bill will increase unemployment. And having opted to make both jobs and foreigners central planks of its electoral campaign, it has no intention of letting the legislation pass without a fight.

But correspondents say it needs to proceed with care.

The president of the German Industry Association, Michael Rogowski, told the CDU at a key party congress earlier this week that they needed to take a more "reasonable" line on immigration.

The country, he said, needed skilled workers and needed them soon if it were to compete effectively on the international stage.

And surveys show that while more than half of Germans feel there are too many immigrants in the country, a similar number - including Christian Democrat supporters - are in favour of opening the doors to skilled immigrants.