Here's just a few incidents that have happened due to wearing gloves near moving machiners. They should never be worn. Ever.
My approach would be to have a quiet word with him. Tell him to google "glove caught in machinery" or "machinery caught accident". For specific OSHA stuff google "OSHA caught accident".
"A maintenance worker was busy scrubbing and spraying down the extruder intake hopper when his glove became caught in the rotating rolling pins (Photo 1). The rollers slowly sucked in his glove, fingers, hand, and eventually his arm, up to the mid-bicep. The wound was so grave his arm was ultimately amputated."
"A machine operator died when his glove caught in the wire that was being spooled onto a drum of a wire drawing machine. The victim was pulled between the drum and the machine housing. The machine did not have any guarding around the drum. The company had no operating or safety instructions for the safe operation of the machine. The victim reached into the machine while it was running"
"Drilling a pole, drill bit caught leather glove- fracture little finger."
"Using picking tool on sorting table, glove got caught in picker. Amputation right index finger."
"His hand got just a bit too close to the spinning wheel. His glove got caught and his hand got sucked into the chopper. There was no shut off switch close by. A fellow deckhand heard the scream and ran over to shut off the bait chopper. By that time, Brian had lost his thumb and about half of his hand."
"Mays stated he was trying to free the lodged drill steel by twisting the extension with his right hand. He then inadvertently struck the rotation lever with his left hand. He stated that both bones in his right forearm were broken and the first joint of his right little finger which was partially severed had been reattached.
Mays remained off work and began physical therapy after his injuries were sufficiently healed. However, due to pain in his right hand, additional surgery was performed on October 29, 1999 at the Clinch Valley Medical Center. Mays was scheduled to be released from the hospital on October 31, 1999. However, on the morning of October 31, 1999 Mays was found dead in his hospital room. "
"As the plate was fed in a razor sharp, needle pointed shear "spike" (Where the
shears took a double cut) about three inches long, lying close enough to the
edge to escape notice, caught the wrist band of the man's glove.
As I watched from thirty feet away, and in the time it took me to react, and
cross the intervening distance, the plate pulled him in THROUGH the guard and
pull his hand his arm AND the crumpled remains of the guard and it's Angle iron
frame inexorably into the zero gap between the roll and the plate.
I reached him and punched the "Big Red One" as his shoulder and chest started to
crunch and collapse. During all this time he didn't utter a sound and his mate,
around the other side of the plate was totally unaware of any problem until he
came around to see why the machine had stopped!
As I hit the stop I grabbed him to prevent him from falling as he lost
conciousness. My Job, for the next 40 minutes, was to hold him upright as the
millwrights tore the machine apart to free him. For twenty of those minutes I
listened to the crackling, gurgling of his slowing breathing, in and out of his
half crushed chest.
For the remaining twenty minutes I gently cradled a dead man..to stop his face
from getting all dirty."