回复：办GC时需要以前中国雇主的证明信吗？

It depends on. If the AD your employer posted on the newspapers indicated that ? of years experience is required or desired, you may need to get the letters from your previous employer(s). My lawyer suggested me to get the letters from my previous employers because the AD my company posted indicated 3 years experience is required. The letter must show your title and working experience that is similar and/or relevant to the current position you are on, on the paper with company's letterhead, and signed by the person in-charge. If the AD doesn't mention working experience is required or desired, you don't need to worry about the employment letters for RIR or LC. I was told that the employment letters may be required for I-140, I am not sure as I haven't been gone that far.