Freelance Turkey (Istanbul)

Hi,

I had a meeting today where I was told that the only way I can get paid by this particular company, since they aren't hiring employees, is if I send them an invoice for my work. I am a Turkish American citizen and don't reside in Turkey full time but they are saying that I cannot invoice them as a foreigner. I'm not really sure what to do... I have never worked under such conditions in Turkey before...