25 Pa. Stat. § 2862
All candidates of political parties, as defined in section 801 of this act, for the offices of United States Senator, Representative in Congress and for all other elective public offices within this State, except that of presidential electors, shall be nominated, and party delegates and alternate delegates, committeemen and officers who, under the provisions of Article VIII of this act or under the party rules, are required to be elected by the party electors, shall be elected at primaries held in accordance with the provisions of this act, except as otherwise provided in this act. In the years when candidates for the office of President of the United States are to be nominated, every registered and enrolled member of a political party shall have the opportunity at the Spring primary in such years to vote his preference for one person to be the candidate of his political party for President.
25 P.S. § 2862