看到一些帖子说拿到绿卡后180天才能为另一家公司工作，
-Just rumor.
并且在您的回帖中提到拿到绿卡后将回到A公司工作, 我朋友为什么能不回到A公司而继续留在B公司呢？
-He had better go back to work for Company A, but if his boss does not care about it, it will be fine because he had worked for Company A before. Also, the Company has the right not to hire him back even if the company sponsor him green card. But if his boss insist that he has to work for Company A and thus file a lawsuit, he might have some problem (it does not mean he will lose the lawsuit because he also has the right to resign the job). Th job is at will. Anyway, I do not find any immigration law specifically address this issue. The immigration law just say the employer has the intent to hire the employee after the employee get the green card and the employee also has the intent to work for the employer after getting the green card. The only issue is how to prove the intent, not have to work. Of course, working for the I-140 sponsor for a while (either before or after getting the green card) is the best proof to have such the intent. Just like we apply for the F-1 visa and have to prove we do not have the immigration intent, but it does not mean we are not allowed to get the green card after stay in US for a while.
