My question is about Muslim immigrants to non-Muslim countries. I have heard an opinion that states that it is Haram for Muslims to immigrate to non-Muslim countries if there is no vital need to do so. Then there is the opinion that if they immigrate for a Halal reasons (such as bettering their life) then it all right but if they immigrate for a Haram reason (such as to drink alcohol easily) then the immigration is Haram.
My question is these Muslims who immigrated from Muslim to non-Muslim countries, if their immigration is Haram either because of the opinion that states that this immigration in itself is Haram or because they may have immigrated for a Haram reason, is the money that these Muslims make from their jobs in non-Muslim countries (as long as their jobs are Halal) Halal or Haram?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

Basically, migration from Muslim countries to non-Muslim countries is forbidden in the Sharee’ah. But, it is allowed in some exceptional cases when a person is compelled to migrate there because he does not have any other choice. For instance, if one fears for his soul and does not find any Muslim country where he can take shelter, or similar situations, it is permitted for him to migrate to a non-Muslim country. This rule is for the one who wants to settle there permanently but the same rule applies to the one who intends to stay there temporarily. Staying there even for a short period is not permissible except for a valid reason such as to get treatment, or to get some knowledge not found in Muslim countries, or to preach Islam, or to teach Islamic Sharee’ah to the Muslims who live there, etc.

But, going there only for a material purpose is not permissible since there is a high risk for the religion of the Muslim and his worldly life, as it is well known for every wise person.

As for the earnings of the Muslims in those countries they are lawful if one earns them through working in legal field. If one indulges in selling unlawful things, such as selling pork, alcohol, dead animals, etc. then the earnings are unlawful.

Therefore, he should get rid of those unlawful earnings by spending them for the benefit of Muslims such as establishing hospitals, etc.

Allah knows best.