More than 20 school districts in the United States have been equipped with military-grade equipment through the federal program that provides such gear to local and state authorities free of charge, according to civil rights groups.

The NAACP Legal Defense Fund and Texas Appleseed, a legal advocacy group, sent a letter on behalf of a coalition of civil rights groups to the federal agency that administers the program on Monday. The letter requested reforms be made to the 1033 program, which has come under significant scrutiny after the heavily armed police response to protests in Ferguson, Mo., last month.

The letter cited “published reports” that have showed military equipment being transferred from the Pentagon to the school districts. It said the total number of transfers from the Defense Department to U.S. schools “is difficult to determine.”

KPBS in Sand Diego reported that the city’s school district had received a mine-resistant vehicle. KTLA in Los Angeles reported that the district there had also received its own mine-resistant vehicle as well as grenade launchers. KHOU in Houston reported that local school districts had received military firearms.

A school district in Edinburg, Texas, has employed a full SWAT unit, according to the letter, which is equipped through the 1033 program. The groups pointed to a news image that showed officers in military fatigues standing in front of school buses.

“It is frankly difficult to imagine how a grenade launcher, or any of these items, could be safely used in any scenario involving schools,” the letter said.

School districts in Texas, California, Florida, Georgia, Kansas, Michigan, Nevada and Utah have received military equipment, according to the groups.

“Taxpayer dollars should be steered away from investments in increased law enforcement and militarization of schools and towards supporting solutions that address the root causes of school safety concerns and provide students with the services and supports they need to succeed,” the letter concluded.

In the wake of the Ferguson protests, President Barack Obama has reportedly ordered a review of the 1033 program and others. Congress is also holding hearings on the programs this month.