If voters in the heavily-Democratic district cast their ballots for former congressional staffer Lindsay Powell, Democrats will keep the slight majority they previously had.
The party has defended its majority in a series of special elections since November.
With either outcome, Pennsylvania's government will remain divided with Democrat Josh Shapiro in the governor's office and Republicans holding a Senate majority.
With control over the calendar, Democrats have advanced a number of their priorities on a one-vote margin.
If Republicans gain control of the House, they can take some of these questions to voters through proposed constitutional amendments without Shapiro's approval.
Persons:
Lindsay Powell, Erin Connolly Autenreith, Josh Shapiro, Powell, “, that’s
Organizations:
—, Pennsylvania’s, Pittsburgh, Democratic, Republicans, Republican, Senate Republicans
Locations:
HARRISBURG, Pa