Voters in a dozen Virginia House of Delegates districts have filed a federal lawsuit challenging a legislative map that they say illegally concentrates African American voters and therefore dilutes their influence.

The lawsuit — first reported by the political blog Blue Virginia — was filed last week in the U.S. District Court for the Eastern District of Virginia. It follows an October decision by the court that declared the state’s congressional maps unconstitutional because they “pack” African American voters into a single district. Congressional Republicans have appealed that decision.

Speaker of the House of Delegates William J. Howell (R-Stafford) said Wednesday that he was confident the state’s legislative map would withstand legal challenge.

“The House districts were drawn in accordance with all federal and state law, adopted with bipartisan support after more than a dozen public hearings and committee meetings, and pre-approved by President Barack Obama’s Justice Department in accordance with the Voting Rights Act,” Howell said.

He said the map was “publicly supported by a majority of African American members in the House of Delegates.”

Attorney General Mark R. Herring (D), through a spokesman, declined to comment on the Dec. 22 lawsuit, which names the election commissioner and the Board of Elections as defendants.

Both the congressional lawsuit and the state-focused lawsuit were filed by lawyers from the Washington law firm Perkins Coie, who were unavailable for comment Wednesday.

The cases follow a 2013 Supreme Court decision invalidating a key provision of the Voting Rights Act that had required some states with a history of discrimination to not draw districts in such a way that created a “retrogression” in minorities’ ability to elect their preferred candidates. That generally meant not breaking up districts with a majority of black voters.

Although the Voting Rights Act was meant in part to ensure elected representation for minorities, Democrats have argued in recent years that Republicans have used the act and its provisions to justify diminishing black — and Democratic — influence outside of the majority-minority districts.

The suit filed last week claims that the redistricting process by Virginia’s House in 2011 resulted “in bizarrely shaped and highly non-compact districts that cross natural geographical boundaries and split political subdivisions with impunity.”

Last week, a study group created by Virginia Gov. Terry McAuliffe (D) recommended an overhaul of how districts are drawn in the state in hopes of reducing the influence of politics on the process.

McAuliffe declined to comment directly on the lawsuits, saying through a spokeswoman that the study group’s plan “is the best way to put Virginians’ voices ahead of partisan politics.”