(CNN) Four aid volunteers are facing prison time after leaving food and water inside an Arizona national wildlife refuge where undocumented migrants have died trying to enter the United States.

The volunteers, who are part of the No More Deaths ministry of the Unitarian Universalist Church of Tucson, could be sentenced to up to six months in prison and fined up to $500 after they were convicted Friday by Federal Magistrate Bernardo Velasco.

The volunteers -- Natalie Hoffman, Oona Holcomb, Madeline Huse, and Zaachila Orozco -- were charged with entering a national wildlife refuge without a permit and abandonment of property, according to a statement from the aid group.

Five other No More Deaths volunteers face charges for "efforts to place life-saving food and water" inside the Cabeza Prieta National Wildlife Refuge, the aid group said. Those volunteers will have trials in February and March.

Cabeza Prieta is Arizona's largest wilderness area, spanning 803,418 acres of isolated and rugged landscape of the Sonoran Desert. A joint investigation was launched by US and Mexican authorities in 2001 after at least 14 migrants died in a single incident after crossing the border in the refuge. They probably were abandoned in the desert by people smugglers, authorities said at the time.

No More Deaths says 155 migrants have died in the area since 2001.

No More Deaths aid volunteers found guilty of trespassing after leaving food and water at border

Jugs of water and cans of beans

Hoffman was also charged with operating a motor vehicle in a wilderness area. The offenses are all misdemeanors. A sentencing date was to be set within the next week.

"This verdict challenges not only No More Deaths volunteers, but people of conscience throughout the country," No More Deaths volunteer Catherine Gaffney said in a statement. "If giving water to someone dying of thirst is illegal, what humanity is left in the law of this country?"

Velasco said in his ruling that the refuge is "littered with unexploded military (ordnance), the detritus of illegal entry into the United States, and the on-road and off-road vehicular traffic of the US Border Patrol." He also noted that the water and food left by volunteers "erode the national decision to maintain the Refuge in its pristine nature."

One of the volunteers still awaiting trial is Scott Warren, who the group said also faces charges of felony harboring and conspiracy related to his "humanitarian aid work." His trial will be in late May.

An affidavit in support of the summons for Hoffman, Holcomb, Huse and Orozco said the four volunteers entered the designated wilderness area without authorization in August 2017 to leave gallon jugs of water and cans of beans.