Chinese workers in Israel are forced to agree not to have sex with or marry Israelis as a condition of getting a job.
According to contacts they are required to sign, male workers may not have any contact with Israeli women - including prostitutes, a police spokesman, Rafi Yaffe, said.
An Israeli lawyer said that a Chinese worker will agree to anything and will not have anyone to help them if there is a problem.
The labourers are also forbidden from engaging in any religious or political activity. The contract states that offenders will be sent back to China at their own expense.
Foreign workers from Thailand, Philippines and Romania, say they are subject to almost slave conditions, and their employers often take away their passports and refuse to pay them.