CHARLOTTE, N.C. —  Charlotte-Mecklenburg Schools is pausing the rollout of clear backpacks for students after discovering a label that warns of potentially cancer-causing chemicals. 

The school district planned to distribute thousands of clear backpacks to high schoolers this spring in response to guns on campus. 

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"Students will be required to carry clear backpacks at schools as the program is launched to discourage prohibited items on campus," the district posted in early March. CMS' iMeck Academy was set to be the first school to implement the rollout, followed by Hopewell High School. 

The backpack distribution was delayed "out of an abundance of caution" due to the discovery of a Proposition 65 warning label, CMS said Monday. The label is on items that may contain cancer-causing chemicals. 

The California Office of Environmental Health Hazard Assessment says Proposition 65 requires businesses to provide warnings about significant exposures to chemicals that cause cancer, birth defects or other reproductive harm.

"In unloading clear backpacks for distribution at the two pilot schools, we discovered most backpacks contained a warning tag required by Proposition 65 for California residents. We immediately paused the rollout of this safety measure when it was revealed the majority of the inventory had the tag," Eve White, executive director of communications for CMS, said in an email Monday. 

The school district purchased 46,000 clear backpacks, with a total cost of $441,791, the Charlotte Observer reports.

The implementation of the backpacks was part of Charlotte-Mecklenburg Schools' approach to tackle safety on campus. 

Eddie Perez, a media relations specialist for CMS, told the Observer that 25 firearms have been found on campuses this school year.

December data from CMS shows guns were recovered from at least 13 different schools throughout the district. CMS Superintendent Earnest Winston released an urgent video message in December asking for families to help stop the pattern of bringing guns to school.

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The district plans to continue training for security scanners and hire additional campus security. 

In February, CMS activated the Say Something Anonymous Reporting System in middle and high schools. The system encourages students and adults to tell a trusted adult directly about a potential threat, or submit a tip anonymously via the Say Something app, at www.saysomething.net or by calling 1-844-5-SayNOW. 

CMS says they are contacting the manufacturer of the backpacks and will not proceed with distribution until the matter is resolved.