Pa. Const. art. VII, § 6

All laws regulating the holding of elections by the citizens, or for the registration of electors, shall be uniform throughout the State, except that laws regulating and requiring the registration of electors may be enacted to apply to cities only, provided that such laws be uniform for cities of the same class, and except further, that the General Assembly shall by general law, permit the use of voting machines, or other mechanical devices for registering or recording and computing the vote, at all elections or primaries, in any county, city, borough, incorporated town or township of the Commonwealth, at the option of the electors of such county, city, borough, incorporated town or township, without being obliged to require the use of such voting machines or mechanical devices in any other county, city, borough, incorporated town or township, under such regulations with reference thereto as the General Assembly may from time to time prescribe. The General Assembly may, from time to time, prescribe the number and duties of election officers in any political subdivision of the Commonwealth in which voting machines or other mechanical devices authorized by this section may be used.