Police argue the measures are needed to stop work permit abuses and to stem a flood of women coming to the canton from countries such as Poland, Hungary or Slovenia.

At the same time, a campaign has been launched against forced prostitution during the Euro 2008 football tournament hosted by Switzerland and neighbouring Austria.

Experts say there is growing concern at the rising number of women sex workers taking advantage of a bilateral agreement between Switzerland and the European Union granting unlimited access to each other's labour markets.

From June 1 this year prostitutes from the new EU countries, particularly in central and eastern Europe, have not been issued work permits for canton Zurich. Instead the jobs went to Swiss women or those from the "old" EU states.

Brothel owners must now prove that they have tried to fill vacancies from the latter category of women before they can employ eastern European sex workers on a temporary L residence permit.

Employers have labelled these new regulations as unworkable.

The Zurich women's advice group, Fiz, claims eastern European women will now be forced to work illegally on the streets where they will be at the mercy of violent customers and prone to exploitation and trafficking.

Numbers increasing
"This is creating two new classes of sex workers," Fiz spokeswoman Susanne Seytter told swissinfo. "This is a repressive regulation and will not solve the problem."

The problem, as the cantonal authorities see it, is that too many women from eastern Europe have been flooding into the area since Switzerland voted to open its borders to workers from the new EU states in September 2005.

The canton registered enough workers from this region ? mostly in the sex industry : to cover 2,000 working days in October 2006, but by March this year that number had risen to 5,000.

In addition, it is claimed that many of these women and the brothels that employ them have been sidestepping the criteria for issuing these temporary L permits.

Switzerland negotiated a clause in the 2005 bilateral agreement allowing it to set quotas on workers from new EU states until at least 2011.

A women's pressure group on Thursday also started a campaign against forced prostitution and human trafficking that will run up to the start of the European championships in June 2008.

Courage displayed
Many women, notably from eastern Europe, were forced into prostitution during last year's World Cup in Germany, according to human rights groups.

Under the slogan "We Show Civil Courage" the collaboration of women's organisations, church groups, businesswomen and politicians aims to highlight the plight of hundreds of thousands of women who are forced into the sex industry in Europe.

"We are making forced prostitution an open subject," said spokeswoman Renata Böhi:Reck, who called on people to have the courage to report such practices to the police.

Swiss President Micheline Calmy:Rey and Economics Minister Doris Leuthard are also supporting the campaign. It claims to have gathered the support of a million Swiss women.

swissinfo, Matthew Allen in Zurich with agencies

NZZ Online, Switzerland