As a researcher in a pharmaceutical company with a PhD degree in Biology and in H-1B status for 2 years, I want to apply for U.S. Green Card in EB1 (EB1 Extraordinary Ability, EB1 Outstanding Researcher) or EB2 National Interest Waiver (EB2 NIW) immigration categories, or apply for 2 categories at the same time. 

It is very difficult for me to get reference letters form U.S. government agencies or some professional societies. Do I have to get reference letters for those applications? and are there any thing more I should know about the reference letters? 

There are many issues to be addressed about reference letters or recommendation letters. First, the reference letters are not required by USCIS. But they can be very useful, and most USCIS examiners for EB1 Extraordinary Ability, EB1 Outstanding Researcher or Professor, or EB2 National Interest Waiver application expect them. 

Some alien applicants may try to avoid the reference letters or recommendation letters for confidentiality purposes, but for others, they are easy to obtain the reference letters. Some professional societies usually do not provide reference letters of their members. In addition, U.S. government agencies will normally not simply prepare a reference letter if asked. So the request of reference letters or “independent letters” heavily favors applicants with connections at government agencies or in professional societies, which may see as unfair for some applicants.

If it is difficult for an applicant to get reference letters or recommendation letters, a more thorough compilation of background materials can offset an absence of reference letters. These materials may include statistics about the area of research, information about professional organizations, awards, journals, etc.