35 Miss. Code R. § 3-11-09-101
Nonresident employees rendering services exclusively in Mississippi are subject to withholding computed upon total wages received, as in the case of a resident. If the nonresident's services are performed partly within and partly without the state, only wages paid for services performed within Mississippi are subject to withholding. The burden and duty is placed upon the employer to determine the place of residence of each employee, and to determine the exact part of each employee's earnings which is attributable to services performed within Mississippi and to apportion such earnings accordingly for the purpose of withholding the tax. When a nonresident officer or employee of a corporation has his base situs in Mississippi and earns his salary, wages, or commissions while assigned to or traveling from the Mississippi base, the total wages received incident thereto are subject to Mississippi withholding.
35 Miss. Code. R. § 3-11-09-101