Grapevine: Schumacher Home in Pay Row

Instead, the 36-year-old German has been caught up in a row over union laws, international labour treaties and the minimum wage after it emerged that French and German labourers working on his 35 million Swiss franc ($28 million) villa had been paid substantially less than the Swiss minimum.

The use of cheap foreign labour on a building site would normally be of little public interest.

Unfortunately for Schumacher, the "Schumiland" story emerged just as the Swiss began to contemplate a national vote on Sept. 25 on whether to make it easier for immigrant workers, mainly from eastern Europe, to get jobs in wealthy Switzerland.

The Swiss parliament has already approved the expansion of Switzerland's labour agreement with the EU to cover the Union's 10 new member states, but opponents were able to gather enough support to force the popular vote.

A Sunday opinion poll by Le Matin newspaper showed a margin of just three percent between the "yes" and "no" camps, so the Schumacher affair may have emerged at just the right moment for those opposing the expansion.

The construction company involved in building the villa has already said that it unwittingly underpaid six French stonemasons and has since increased their wages.

Schumacher's Geneva-based lawyers were not immediately available for comment, but insisted in local reports on Tuesday that the Ferrari driver was completely unaware of the situation.

That has not spared him from some unsavoury headlines.

"Slaving for a pittance," read the front page of Switzerland's best-selling Blick newspaper on Monday, while Tuesday's Le Matin described the news as a "scandal."

The biggest Swiss trade union group, Unia, is urging members to vote in favour of expansion - although it was Unia officials who drew attention to the situation at Schumacher's villa.

"We believe that cases like Schumacher's actually prove that the controls to prevent wage dumping are working," Unia spokesman Hans Hartmann told Reuters. "Of course it's true that some people might just see the Schumacher headlines and think that's a reason to vote against further expansion, but that would be the wrong reaction.

"We believe in a 'yes' vote mainly because we believe in people's basic right to work wherever they choose, but also because we have already used the surrounding debate to get much better conditions for all workers here - no matter what their nationality."