To work in the United States, most immigrants require a work permit.
The employment authorization document (EAD) also known as work permit, is a document issued by the Citizenship and Immigration Service (USCIS), which grants non-citizens temporary authorization to work in the United States.
Unlike non-citizens, both US residents and citizens can work without this document. For example, one of the benefits of Deferred Action (DACA) is that eligible Dreamers can access an EAD.
Other non-citizens eligible to work in the United States and process their EAD are: asylees, refugees, U Nonimmigrants, legal permanent residents, certain foreign students, summer jobs, among others.
On the other hand, as mentioned above, legal permanent residents do not need to apply for an EAD, since their Green Card or Form I-551 is valid as employment authorization. Likewise, temporary workers, with H-1B, L-1, O or P visas, do not need to apply for an EAD, since their visa authorizes them to work in the United States only for a specific employer.

This document is processed through the USCIS by filling out Form I-765, Application for Employment Authorization. Eligibility to obtain an EAD is divided into three categories: persons authorized due to immigration status, persons authorized due to a specific employer, and immigration category requiring an application for an EAD.
In this sense, when hiring a foreign worker, employers must ensure that they have authorization to work in the United States for a specific period of time, otherwise their hiring will be impossible. That is, you have an EAD and have completed Form 1-765. click here for more information about the form.
It is worth mentioning that the filing fee for the corresponding form is $410, however, there are exceptions. In addition, for example, DACA beneficiaries must complete another payment of 85 dollars corresponding to the collection of biometric data.
Learn more about this process at the following link: https://www.uscis.gov/es/formularios/explorar-mis-opciones/como-solicitar-un-documento-de-autorizacion-de-empleo