They argued that the populations of the districts have shifted so much in the past decade that using the previous boundaries would be unconstitutional, violating the "one person, one vote" principle of districts of roughly equal size.
Republican leaders would prefer to allow the Legislative Reapportionment Commission the time necessary to come up with a map that passes muster, even if that means moving the primary to June or July.
Senate Majority Leader Dominic Pileggi, a Delaware County Republican, said last week that the legislature would be willing to change the date.
Pileggi and Minority Leader Mike Turzai (R., Allegheny) were the main plaintiffs seeking a restraining order Monday from U.S. District Judge R. Barclay Surrick. The judge did not say when he would rule.
A three-judge panel of the U.S. Court of Appeals for the Third Circuit could ultimately decide whether using the 2001 map would be legal.
Democratic leaders - Senate Minority Leader Jay Costa and House Minority Leader Frank Dermody - want the election to proceed on time, arguing that the primary campaign season has already begun.
Under state law, candidates for the legislature have just three weeks - from Jan. 24 to Feb. 16 - to collect hundreds of voter signatures to get onto primary election ballots. At least 300 voter signatures are needed to get onto the ballot as a House candidate, and 500 valid signatures for the Senate.
Those signatures then can be challenged in court.
Without knowing the boundaries of each district, it's impossible to say whether a signature from any given voter would be valid. The candidates would not know if the voter - or, for that matter, the candidates themselves - lived in the appropriate legislative districts.
Clifford Levine, the attorney for Costa and Dermody, said that since the 2001 map was the only valid one remaining, "it is clearly rational to proceed under" that plan.
He also said the Republicans' request for a restraining order was odd. Normally, he said, restraining orders are granted to maintain the status quo while an issue gets resolved.
"They're not asking for the status quo," he said. "They're asking to blow up the election."
Latino voter advocates also joined the fight Monday, favoring the reapportionment, which increased Hispanic majority districts from one to four and reflected their growing numbers across the state.
Using the 2001 map could disenfranchise those voters, said Juan Cartegena, from LatinoJustice, a Latino civic-advocacy organization.
"Latino voters need to know any plan is going to reflect the demographic changes," he said.
Contact staff writer Troy Graham at 215-854-2730, firstname.lastname@example.org, or @troyjgraham on Twitter.