Ulster number eight Nick Williams has been cited for his attack on Rhys Patchell in their win over Cardiff Blues on Friday.
The 31-year-old was sin-binned at the time as he came in with a forearm to Patchell in a maul, although he seemed fortunate to avoid a red card.
He could face a suspension however after being cited for the offence.
An official statement read: "Nick Williams, the Ulster No.8, has been cited by an independent citing commissioner for allegedly striking an opponent in the Guinness PRO12 match against Cardiff Blues at Kingspan Stadium, Belfast last Friday.
"Law 10.4 (a) – Punching/striking. A player must not strike an opponent with the fist or arm, including the elbow, shoulder, head or knee."