PITTSBURGH — The increasingly nasty election battle between two Democratic congressmen in southwestern Pennsylvania might hinge on which place a judge determines is the legal residence of a young campaign staff worker: her parents’ home, or an apartment she shares outside of the congressional district.

Rep. Mark Critz and Rep. Jason Altmire are seeking election to Pennsylvania’s newly redrawn 12th District, created by Republicans who control Harrisburg to force the men into a primary contest during the once-a-decade process of revising boundaries to reflect population shifts.

The dispute landed in court Friday, and Commonwealth Court Judge Dan Pellegrini said he would rule on the matter as early as Monday. His decision could knock Altmire’s name off the ballot, potentially ending Altmire’s bid for a fourth term in Congress.

Critz, who is serving his first full term, claims that about 200 petition signatures submitted by Altmire’s campaign aren’t valid because a young staff worker who collected them shares an apartment outside of the district. If Critz succeeds in getting those petitions thrown out, Altmire would be left with about 950 signatures, or less than the required 1,000, a spokesman for Critz said.

But Pellegrini questioned a key aspect of that argument during the hearing, noting that Altmire’s campaign worker is a registered voter in the 12th District.

David Montgomery, Altmire’s lawyer, also presented dozens of pieces of evidence showing that the 23-year-old campaign worker still lists her parents’ address in O’Hara Township on her driver’s license, bills, paystubs and checks. The suburban Pittsburgh home is inside the 12th District.

Scott Caulfield, Critz’s lawyer, questioned whether the campaign worker actually sleeps at her parents’ house on most nights, as opposed to an apartment she shares in Pittsburgh, which is outside the district.

The law requires candidates for U.S. House to submit the signatures of 1,000 registered party voters to get on the primary ballot. The Altmire campaign had originally presented 1,651 signatures, but Critz successfully challenged hundreds of them as invalid.

The primary is April 24.