Who Doesn't Need To Apply Separately For A Work Permit:
Students can work under certain circumstances, but they must get permission from an authorized school official at the school or college. Your immigration attorney can explain how a green card works, too. All green card holders can work in the United States by presenting their green cards to their employers. Immigrants who later become U.S citizens will be able to show their passports or naturalization certificate to employers as a verification that you are legally able to work.
Special Note: All employees, including U.S. citizens and permanent residents, need to prove their ability to work here in the U.S. When you get legal help, you should ensure you receive an Employment Authorization Document (in most situations not involving a nonimmigrant visa), which is proof to show any employer that you are legally allowed to work in the United States. And that includes students, refugees, spouses and fiancés of U.S. citizens who have not yet obtained their lawful permanent residence, and all foreign nationals.