Calvin Munerlyn, 43, was shot in the back of the head on Friday at the Family Dollar store in Flint, Michigan, one of the US states hardest hit by the pandemic.
He was attacked after telling 45-year-old Sharmel Teague’s daughter she could not come into the shop without a state-mandated mask.
The mother’s husband, Larry Teague, 44, and son, Ramonyea Bishop, 23, are accused of going to the store shortly afterwards and fatally attacking Mr Munerlyn.
Sharmel Teague has been arrested, but the two other suspects remain at large. All three face first-degree premeditated murder and firearms charges.
Larry Teague is also charged with violating the governor’s order requiring face coverings inside stores in order to prevent coronavirus transmission.
Her daughter has not been charged.
After the initial verbal altercation at the store, Genesee County Prosecutor David Leyton told a news conference on Monday, Sharmel Teague shouted at and spat on Mr Munerlyn before driving away in a red GMC Envoy.
She returned a short while later with her son and husband before the fatal confrontation ensued, according to officials.
It was the son who allegedly pulled the trigger.
The prosecutor told reporters: “The death of Calvin Munerlyn is senseless and tragic, and those responsible will be held accountable to the fullest extent of the law.”
Mr Munerlyn’s mother, Bernadett, told the Associated Press news agency: “All my baby was doing was his job.”