Hiring of Foreign Nationals already on H-1Bs with other employers
Often employers will hire new candidates who are already on H -1B visas sponsored by another employer. In this instance it is required for the new employer to submit an H-1B visa petition to the INS for the employee. For the employee, this will amount to an extension of their current H-1B visa.

One benefit to hiring this type of candidate is that the employer may commence employment as soon as the visa petition is filed with the INS. Because the individual is already on an H-1B visa, there is no need to wait for INS approval of the new petition to start employment.

Persons entering United States on an H-1B visa are eligible to remain in the U.S. for a maximum of six years. Upon the attainment of six years in H-1B status, the foreign national is required to return home for one year prior to reentering the United States as an H-1B visa holder. More on H-1Bs