20 Pa. C.S. § 767
In any proceeding where the orphans' court division considers that the interests of any taxing authority, including the United States, any state and any political subdivision thereof, may be adversely affected directly or indirectly by a decision of such division because of the effect of such decision on assets subject to tax or for any other reason, the division shall have the power on its own motion or on the application of any party in interest, including the taxing authority, and upon such notice as it may direct, to authorize the taxing authority through its proper officer to appear as a party in interest, and if such an appearance is entered, the taxing authority shall be considered to be a party in interest aggrieved by any decision adversely affecting its interests.
20 Pa.C.S. § 767