(a) Every employer maintaining an office or transacting business within this Commonwealth and making payment of compensation (i) to a resident individual, or (ii) to a nonresident individual taxpayer performing services on behalf of such employer within this Commonwealth, shall deduct and withhold from such compensation for each payroll period a tax computed in such manner as to result, so far as practicable, in withholding from the employe's compensation during each calendar year an amount substantially equivalent to the tax reasonably estimated to be due for such year with respect to such compensation. The method of determining the amount to be withheld shall be prescribed by regulations of the department.
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