US employers have the option of employing non-immigrant workers on a temporary but long-term basis on H-1B or L1 visas. However, if they wish to employ foreign workers on a permanent basis, a complex process of acquiring a green card begins. The first step in this process is usually labor certification. If there are qualified US workers, even minimally qualified US workers - then the foreign worker cannot be offered the position on a permanent basis. This does not necessarily mean that the foreign worker will be immediately replaced by a qualified US worker, though. The foreign worker can still serve out the remainder of their existing temporary visa in the US, and may well be able to re-apply for labor certification and be approved. But it does create a substantial inconvenience for the US employer who wishes to hire a foreign worker, and provides some protection to US workers.
A permanent labor certification issued by the Department of Labor (DOL) is most often the first step in allowing an employer to hire a foreign worker to work permanently in the United States. In most instances, before the U.S. employer can submit a petition to the Department of Homeland Security’s U.S. Citizenship and Immigration Services (USCIS) seeking to hire a foreign worker as an immigrant, the employer must obtain an approved labor certification from the Employment and Training Administration. The Department of Labor must certify to USCIS that there are no U.S. workers able, willing, qualified, and available to accept the job and that employment of the alien will not adversely affect the wages and working conditions of similarly employed U.S. workers.