Under the United States immigration law, an employer has the right to hire workers from foreign countries if the Department of Labor believes that the employment of such workers will not adversely affect the wages and working conditions of U.S. workers of the same occupation in the employer's locality.

This is generally referred to as the labor certification process.

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Generally, a labor certification is obtained upon the application of a particular employer who persuades the Department of Labor that the employer has made a bona fide effort to recruit U.S. workers.
This is usually accomplished by listing job openings in the newspaper of general circulation.
After a recruiting period of 30 to 45 days, the employer then submits a report to the Department of Labor in which he describes his effort to recruit workers. If qualified and available U.S. workers apply for the job, the employer is under no obligation to hire them but should give specific job-related reasons why the persons are unqualified. If a U.S. worker decides that the wage offered is insufficient and does not accept the position, he is considered unavailable.
If the Department of Labor determines that the employer has made a reasonable effort to recruit U.S. workers who are unavailable to him, it will issue the labor certification.
The employer will file a petition with the Immigration and Naturalization Service to establish that a particular alien worker is qualified to accept the position and therefore is eligible for immigration status.
The immigration Service will approve the petition if it believes the employer has a bona fide job opening, is financially able to pay the wage stated in the labor certification and intends to employ the alien worker on a permanent basis.
For this purpose, permanent does not mean forever. It generally means indefinitely.
After the Immigration Service approves the visa petition, the notice of approval is sent to the American Consulate nearest to the alien worker's residence.
The alien worker is then invited to submit an application for an immigration visa which, when approved, entitles him to enter the United States as an immigrant so that he may commence employment for the employer.