Quinn Industrial Holdings has said two of its directors were assaulted in a County Cavan shop on Friday afternoon.
In a statement, the Fermanagh-based company said the two men required medical attention.
They said the attacker fled the scene after staff and members of the public intervened.
Gardaí (Irish police) said they are "investigating an assault which occurred at approximately 1.30pm today in Ballyconnell".
"Two males received facial injuries, which are not believed to be serious.
"No arrests have been made and investigations are ongoing."
Liam McCaffrey, chief executive of Quinn Industrial Holdings (QIH) said: "We are very grateful to members of the local community and to QIH staff who intervened so quickly to stop this vicious physical assault on two of our senior management team as they as they bought their lunch in a local store.
"Cowardly unprovoked attacks of this nature cannot be allowed to go unpunished and we trust the authorities will deal with this accordingly."
The company, comprising of operations once run by Fermanagh businessman Sean Quinn, employs more than 770 people.
Its headquarters are in Derrylin in County Fermanagh, but has operations in the Republic of Ireland and England.