Missouri Gov. Jay Nixon (D) issued a series of vetoes on Monday (Jeff Roberson/AP)

Missouri Gov. Jay Nixon blocked a bill this week that would have allowed specially trained teachers to carry guns in their classrooms.

The state’s Republican-dominated legislature, which overwhelmingly approved the bill, said armed staff members could prevent deadly attacks like the one at Sandy Hook Elementary in Newtown, Conn., in 2012.

But Nixon, a Democrat, argued that arming teachers would not make schools safer.

“I cannot condone putting firearms in the hands of educators who should be focused on teaching our kids,” he wrote in a statement Monday. He said school security should be comprised of “duly authorized law enforcement officers.”

Under the bill, teachers and administrators could be certified as school protection officers after completing a 100-hour police training program. The names of teachers who decide to carry weapons would not be made public, though each staff member would need approval from the school.

The Missouri chapter of the national gun-control group, Moms Demand Action, has strongly opposed the measure and applauded Nixon’s veto.

“Missourians know that asking a teacher to become a sharpshooter won’t prevent another tragedy like Newtown, and we believe that parents have the right to know if there is going to be a gun in our kids’ classrooms,” the group’s co-leader, Melissa Brooks, wrote in a statement.

About one-third of states allow teachers to carry loaded guns in schools, with most districts requiring only permission from from the school.

Arming school staff was the official stance of the National Rifle Association after the massacre in Newtown.

“The only thing that stops a bad guy with a gun is a good guy with a gun,” Wayne LaPierre, the group’s top lobbyist, said days after the shooting. Facing intense national backlash, the NRA later clarified the remarks and declared that each school should decide for itself whether to arm its staff.

The Missouri law also would have lowered the age from 21 to 19 for concealed carry permits and ensured that permit-holders are able to openly carry their guns in any locality across the state.

Nixon, who earned a C rating from the NRA, has previously signed laws that allows schools to teach firearms safety to first-graders – one of the state’s first gun-related laws after Newtown.

Nixon vetoed a total of 33 bills this year, his personal record since coming to office in 2009 and the second-most among any governor in state history. He also rejected a 72-hour waiting period for abortions and bans on electronic cigarettes for anyone under the age of 18.

The legislature has repeatedly clashed with the governor and could override his veto with a two-thirds vote.