Happy New Year. My current employer is filing my I-140 petition. My question is “do I need to submit all US work experience letters?” because my previous employer is not very helpful to provide my work experience letter. I had 4 months of work experience with it on an F1 visa(OPT EAD). Will it be fine if I omit this particular work experience letter when filing the I-140 petition? Also is there any background verification for the work experience submitted for the I-140 petition process?