Restrictions on passport holders for 'Z' Work visa

Hi TravelChinaGuide administrator,

I am a Singapore passport holder and I'd like to check if there are any restrictions on applying for a 'Z' work visa. I seem to notice most, if not, all job advertisements only accepting native English speakers from UK, USA, Canada, Ireland, Australia, or New Zealand, citing reasons of abiding with the Chinese Visa Law. Can I check if this is true? If so, how can I go about applying for a 'Z' work visa then?

Thank you in advance!