The lawsuit, filed Friday, asks a federal judge in Philadelphia to order the state to hold in 2013 special elections that would force lawmakers elected in November to serve shortened one-year terms.
The lawsuit seeks to affect the terms of all 203 House members, who normally serve two-year terms, and the 25 senators in odd-numbered districts who are up for election this year to four-year terms.
The plaintiffs, Joe Garcia, Fernando Quiles and Dalia Rivera Matias, say the population variation in legislative districts drawn in 2001 violates the Equal Protection Clause of the U.S. Constitution and dilutes Latino voting power.
A spokesman for the Pennsylvania Department of State said it would follow any order of the court.
The state's five-member Legislative Reapportionment Commission had been charged with developing a new map of 50 Senate and 203 House districts to go into effect this year and reflect population changes over the past decade.
But in January, the state Supreme Court threw out its initial plan, saying its new map contained numerous splits of municipalities that were not absolutely necessary and districts drawn into shapes that were not properly compact.
As a result, the November election will be held based on the existing map drawn in 2001.
A federal judge previously rejected efforts by the Legislature's Republican majority leaders, Latino groups and others that sought to block the use of the 2001 map in this year's election.
The reapportionment commission eventually approved another plan on June 8, although it still may be challenged in court.