The incident occurred during the Class-A short-season Everett's game in Boise on Thursday.
According to the report, Montero was coaching first base when a scout yelled at Montero to hustle off the field at the end of an inning.
After Montero entered the dugout, the scout ordered an ice cream sandwich and had it sent to Montero. Montero then approached the stands with a bat, cursing, and threw the ice cream sandwich at the scout.
"I am aware of the incident in Boise" Mariners general manager Jack Zduriencik told the Seattle Times. "We are currently in the process of gathering information, but until I have all the details, I cannot comment."
Montero, who is rehabbing from a strained oblique, is hitting .286 with 16 home runs and 74 RBIs in 97 games with Triple-A Tacoma this season.
- Scooby Axson