HARRISBURG — The Pennsylvania Legislative Reapportionment Commission voted Thursday in favor of new preliminary district maps over sharp objections from the House's Republican leader about how his chamber's district lines would change.

The panel voted 5-0 for the Senate plan and 3-2 for the House map.

The passage of the first draft of the new district maps is a pivotal moment in the once-in-a-decade redistricting process, with decisions that will reverberate politically for years to come.

A House GOP analysis showed the lower-chamber's preliminary map would pit incumbent Republicans against each other in at least six districts, while a similar intraparty matchup would occur in just one Democratic district.

All four districts that would have incumbent Democrats and Republicans running against each other had substantially more Democratic voters registered, the House GOP said.

The vote on maps for 203 House seats and 50 Senate seats will trigger a period of public comment and objections. The commission will then produce a final map, after which legal challenges can be made before the state Supreme Court.

The panel that produced the maps consists of the Republican and Democratic floor leaders in both chambers, along with Mark Nordenberg, the former University of Pittsburgh chancellor chosen as chairman by the Democratic majority state Supreme Court.

Nordenberg said the maps reflected two significant demographic trends in Pennsylvania: growing numbers of minorities and a shift in population away from the north and west and toward the south and east.

“It is inescapably true that when population changes require new maps, those maps invariably will affect incumbents, though that was not our goal,” Nordenberg said.

House Minority Leader Joanna McClinton, D-Philadelphia, said the maps reflect that the state's number of Black, Hispanic, Asian and multiracial people grew by more than 800,000 in the past decade, while the white population dropped by about 540,000.

She called it “a representative and fair map.”

But House Majority Leader Kerry Benninghoff, R-Centre, described it as a partisan gerrymander and signaled a possible court challenge.

“Radical change is a problem, when the radical change is rationalized by politics,” Benninghoff said, calling the map “a danger to our system of government.”

An analysis of the map performed for House Republicans concluded it produced 104 to 107 Democratic-leaning districts, which would be eight to 10 seats more than typically emerged from computer simulations. The House majority requires 102 seats.

Nordenberg said the House map had seven “minority opportunity” districts that would have no incumbents and more than 50% minority voters.

“There is no incumbent advantage that will have to be overcome in any of these districts, which would give minority communities residing in them a special opportunity,” he said.

The preliminary Senate map would drastically alter what Democrats saw as the most extreme gerrymanders created by Republicans in the existing map that helped defeat Democratic incumbents in Johnstown and Harrisburg.

The proposed Senate map would remove heavily Republican areas, taking Bedford County out of the Johnstown-based district and Perry County out of the Harrisburg-based district. Both seats are currently held by Republican senators.

Meanwhile, the map would put growing Monroe County into its own district, instead of being split up in what Democrats saw as a Republican attempt to carve out a district favorable to a Republican candidate.

Senate Majority Leader Kim Ward, R-Westmoreland, said she expected corrections before her chamber's map becomes final, “not big changes, but corrections to the map.” She said her favorable vote for the Senate map was designed to keep the process moving.

“It's really been a learning experience,” Ward said. “I've never done this before. I really don't want to do it again.”