(a) When a partnership, estate, trust or Pennsylvania S corporation receives income from sources within this Commonwealth for any taxable year and any portion of the income is allocable to a nonresident partner, beneficiary, member or shareholder thereof, the partnership, estate, trust or Pennsylvania S corporation shall pay a withholding tax under this section at the time and in the manner prescribed by the department; however, notwithstanding any other provision of this article, all such withholding tax shall be paid over on or before the fifteenth day of the fourth month following the end of the taxable year.

(b) This section shall not apply to any publicly traded partnership as defined under section 7704 of the Internal Revenue Code of 1986 (Public Law 99-514, 26 U.S.C. § 7704) with equity securities registered with the Securities and Exchange Commission under section 12 of the Securities Exchange Act of 1934 (48 Stat. 881, 15 U.S.C. § 78a).