The incident went down May 1 but the video -- first obtained by FOX11 -- is just surfacing ... showing 2 men who were apparently transients entering a Target in the San Fernando Valley without face coverings. The men were confronted by store employees. When the customers refused to wear masks, they were reportedly escorted out of the store.

That's when, out of nowhere, one of the customers assaulted an employee ... triggering a full-on brawl, that included another customer trying to help the employees. The melee led to one of the store employees suffering a broken arm. The alleged suspects got away but were located and arrested over the weekend. They face felony battery charges.

The incident prompted the L.A. County Sheriff's Department to tweet, "Please don’t take it out on businesses and their employees when it comes to wearing face coverings. They are trying to uphold the regulations governing their business being allowed to be open. They are having a rough time too."