"Although prostitution is legal in Germany, only Germans are allowed to work in the industry," said Porntip Pakwai of the Empower Foundation, a local non-profit organisation helping to protect sex workers' rights.

Porntip said many sex workers in Chiang Mai had expressed a keen interest in visiting Germany, which hosts the World Cup between June 9 and July 9.

The women believe they stand a better chance of landing a tourist visa to Germany during this season.

Many sex workers prefer to go overseas so they can hide the fact from other Thais that they are involved in the industry.

They are also attracted by the prospect of earning double what they can get here.

"Thai sex workers in a foreign country, though, face risks, especially if they aren't fluent in the language," Porntip said.

Mafia-style figures usually dominate the sex-service industry overseas and often impose unfair working conditions.

"For example, your salary will be the same, but you may be forced to serve many more customers than you agreed to. If you refuse, they may seize your passport or force you to repay them a lot of money claiming that you breached the work terms," she said.

Workers in the sex industry and other fields should keep handy phone numbers of organisations such as the Thai Embassy that they can call for help if necessary. "Also, keep copies of your identity documents," she said.

Before leaving for a foreign country, sex workers should read up on it, she added.