I just had an interview with a new client and they have an ITIN. I verified this number is correct and it is also on the last years tax return as well. On the clients W2 it has a SSN listed and I asked him about it and he said oh that is my number I used for work. I am not sure what to do with this client?  The company who prepared the return last year filed it as is. Do I still file the tax return? I've never come across this before.