HARRISBURG — He no longer owns a residence in Philadelphia and often stays in hotels when he returns, but Lt. Gov. Mike Stack says he has a right to call the city "home" as he runs for reelection.

"I'm a Philadelphian," Stack testified Tuesday during a Commonwealth Court hearing, trying to fend off a legal challenge that could end his bid for another four years as lieutenant governor even before voters have a chance to weigh in.

Where Stack actually lives is at the heart of a dispute that could block him from appearing on the May primary ballot for lieutenant governor. At issue is Stack's decision to list his mother's home address in Northeast Philadelphia in his nominating papers filed earlier this year.

A group of Democratic voters disputes that his mother's house is his primary residence. They say Stack and his wife, Tonya, live in the lieutenant governor's mansion outside Harrisburg.

A decision by Commonwealth Court President Judge Mary Hannah Leavitt could land as early as this week. Among the options, the judge could order Stack to amend the county of residence listed on the ballot.

Stack is facing a crowded field of Democratic challengers in the primary: Braddock Mayor John Fetterman, Craig Lehman of Lancaster County, Montgomery County's Raymond Sosa, Chester County's Kathleen Cozzone, Philadelphia's Nina Ahmad, and Westmoreland County's Aryanna Berringer.

Ahmad is supporting and helping fund the legal challenge to Stack's residency claim, according to her campaign spokesman, Ken Snyder.

A lot is at stake. In a statewide primary, a candidate's county of residence is listed next to his or her name, and Philadelphia is worth plenty of votes. In the 2014 primary, Stack captured 83.2 percent of the vote in the city.

"Philadelphia is not his domicile — his domicile has to be where he lays his head at night … not a place where one has hoisted a flag of convenience," Elizabeth Roggio, a Kleinbard LLC lawyer representing the group of voters, said at Tuesday's hearing, adding that Stack has "misled the voters of the commonwealth."

Roggio and lawyer Shohin Vance, also of Kleinbard, argued that after Stack took office as lieutenant governor in 2015, he and his wife moved furniture and many of their belongings into the taxpayer-funded residence outside Harrisburg for lieutenant governors. The Stacks sold their Philadelphia house in early 2016.

Stack, said Roggio, does not pay rent or a mortgage at his mother's Philadelphia house.

Under questioning by his lawyer, Clifford Levine, Stack testified that his mother's home is the "family nerve center."

"It's the headquarters. It's where we all go," said Stack, who hails from a well-known political family in Philadelphia and who represented a portion of the city in the state Senate prior to being elected lieutenant governor.

Stack's chief of staff, Matt Franchak, testified that shortly after Stack took office as lieutenant governor, he contacted state elections officials for guidance on whether he could register to vote in Philadelphia and that he was told he could use his mother's home address.

Stack said that he has since renewed his driver's license using his mother's address and that he paid the city's wage tax in 2016 and 2017. (It was not clear whether Stack also paid the wage tax in 2015.)

Levine said that once Stack leaves the lieutenant governor's office, Philadelphia is the home to which he will return.

"The reality is that Michael Stack is a Philadelphian," said Levine, of Cohen & Grigsby in Pittsburgh.