William Bamfield, 53, was shot in the left thigh by passengers of another car while he drove an unmarked semi-truck to deliver mail from Farmington to Albuquerque on U.S. 550.
Bamfield was taken to the University of New Mexico Hospital, where he is in stable condition.
"This appears to be attempted murder — I don't think $50,000 is excessive," Postal Inspector Amanda McMurrey said of the reward. "If this helps get somebody who's going around doing random drive-by shootings on the American public off the streets, then that's what it takes."
The mail truck was shot at four times while a dark colored four-door sedan attempted to pass it, New Mexico State Police said. One of the shots ruptured the truck's brake line, forcing Bamfield to stop.
"We value dearly all of our employees and we want to make sure we take every effort that we can," McMurrey said.
Assaulting any postal worker, even contract workers, is a federal crime, but state police have not confirmed what charges will be filed if they make an arrest, she said.
Bamfield told police he saw the car parked on the side of the road, and it turned around to follow him after he passed.
Police believe there were at least two men in the car.
"I don't know if they were targeted or if it's just somebody's sick idea of a joke," State Police Sgt. Andrew Tingwall said. "This has obviously got to stop."
Albuquerque truck driver Victor Delgarito, 51, also reported being shot at by a similar sedan while en route to Farmington where he reported the attack.
State police believe that shooting, which didn't cause any injury, occurred about 30 minutes before Bamfield was shot.
"For somebody within a community to actually shoot weapons at vehicles passing by, I would say that's unusual for New Mexico," Tingwall said.
Police request anyone with information regarding the shootings call State Police Criminal Investigations in Albuquerque at (505) 841-9273.