Under section 512 of the act (53 P.S. § 6924.512), an out-of-State employer who employs a resident of this Commonwealth at a work location outside of this Commonwealth is not required to withhold the local earned income tax. An out-of-State employer may voluntarily agree with the employee to withhold and remit the tax along with the appropriate forms to the tax officer of the tax collection district in which the employee resides. Every employer having a place of business within a tax collection district and employing one or more persons, other than domestic servants, shall withhold the greater of the employee's resident tax or the employee's nonresident tax.
12 Pa. Code § 151.12