61 Pa. Code § 109.8
If a nonresident employe or casual employe, including corporate officers but excluding employes or casual employes provided for in § 109.7 (relating to earnings of salesmen) performs services for an employer or casual employer both within and without this Commonwealth, his income derived from Commonwealth sources includes that proportion of his total compensation for services rendered as an employe or casual employe which the total number of working days employed within this Commonwealth bears to the total number of working days employed both within and without this Commonwealth. However, any allowance claimed for days worked outside of this Commonwealth shall be based upon the performance of services which, of necessity, obligate the employe or casual employe to perform out-of-State duties in the service of his employer or casual employer. In making the allocation provided for in this section, no account may be taken of nonworking days, including Saturdays, Sundays, holidays, days of absence because of illness or personal injury, vacation or leave with or without pay.
61 Pa. Code § 109.8
The provisions of this § 109.4 amended under section 354 of the Tax Reform Code of 1971 (72 P. S. § 7354).