(CNN) -- Democratic Gov. John Hickenlooper of Colorado on Thursday set the date for recall elections for two state senators, marking the first recall effort in the state's history.
On September 10, voters in two districts will have the chance to re-elect or oust their incumbent Democratic state representatives who are being targeted for supporting tougher gun laws in Colorado.
With the help of the powerful National Rifle Association, organizers submitted petitions last month with enough signatures to start the recall process. Earlier Thursday, a Denver district court judge ruled that the petitions met all legal requirements, clearing the way for Hickenlooper to set the elections.
"This is a positive development," NRA spokesman Andrew Arulanandam said in a statement to CNN. "We look forward to working with voters in these legislative districts in Colorado who initiated this effort."
Those leading the effort had to collect enough signatures to equal 25% of the votes cast in the previous election in each district.
For District 11, represented by Senate President John Morse, activists collected 10,137 valid signatures - roughly a few thousand more than the 7,178 signatures required. The district includes Colorado Springs.
For District 3, represented by state Sen. Angela Giron, petitioners collected 12,648 valid signatures, about 1,400 more than required. Giron's district covers Pueblo.
"I'm aware of Chief District Judge Hyatt's ruling and I'm READY!" Giron wrote on her Facebook page. "This last session was my most successful yet, and I'll continue to talk with SD3 residents about our successes. Whether it's an election in September or next year, I'm ready!!! Are you with me?"
Organizers tried but failed to gather enough signatures in two other districts represented by Democrats.
Both Giron and Morse voted in favor of gun control measures that require universal background checks for gun sales and limit ammunition magazines to 15 rounds. Hickenlooper signed the laws into place in March, and they began taking effect July 1, nearly a year after the deadly Aurora movie theater massacre. Colorado's history with mass shootings also includes the bloody attack at Columbine High School in 1999.
Colorado did vote for mandatory background checks for gun show purchases after Columbine and ramped up spending on mental health initiatives after Aurora. But it wasn't until the Newtown elementary school shooting in Connecticut in December that lawmakers in Colorado, as well as Hickenlooper himself, began to seriously take up changes in firearm legislation.
Morse told CNN's Jake Tapper in May, when signatures were being collected, that it was important to remember Colorado was "ground zero" for two of the nation's worst mass shootings.
"We addressed this session, but this is what we get for that response," Morse said.
County Clerks from El Paso and Pueblo counties have estimated the special elections will cost taxpayers between $150,000 and $200,000, according to the Denver Post.
CNN's Steve Brusk and Alison Harding contributed to this report.