Depends if your employee has been authorized to work in the United States under a different non-immigrant work visa such as an H1B specialty occupation Category.
Under the current law, an H1B worker is authorized to accept new employment immediately after the prospective employer files a new petition for non-immigrant alien worker under the H1B specialty occupation Category. The existing H1B employment authorization will continue for the H1B worker until the new petition is adjudicated. However, if the new petition is denied, the employment authorization will immediately end resulting in the H1B employee loss of his employment authorization during all the time an appeal is pending.
Based on the legal consequences of a denial of the new petition, it is important that the alien worker and his prospective employer obtain adequate legal advice regarding the probabilities of
an approval or denial of the alien non-worker H1B petition before the alien worker leaves his or her current employment to start working for the new employer.
There are different statutory grounds that will lead to the denial of the petition. Prior violations of the immigration law for example the employee’s prior employment without authorization at any time after admission in any other category such as student or visitor for business or pleasure that could have occurred at some time in the past but that was not an issue at the time the original H1B specialty occupation was filed and approved but that later comes to the attention of the USCIS at the time of the adjudication of the newly filed H1B non-immigrant worker specialty occupation visa.
In all other situations, the right to legally work in the United States is codified and regulated under the INA and the 8 CFR.
At the present, there are working visas that allow a foreign person to enter the United States to work for a USA employer after a non-immigrant or immigrant work visa petition has been filed and approved.
Most working visas ( non-immigrant and immigrant visas) required a labor certification filed and processed with the Department of Labor prior to the filing of an immigrant or non-immigrant working visa petition.
A worker must be authorized to work pending the approval of an immigrant or non-immigrant working visa before that worker can work without violating the immigration laws and jeopardizing his future right to obtain the approval of the visa for which his employer has filed a petition.
As a general rule, no person can legally work until the application is approved except if the alien has requested and the Immigration authorities have granted permission to accept employment while the application is pending