The 27-year-old was cited after the second of the back-to-back European defeats to Northampton Saints at the Cardiff City Stadium on December 19.
Rees is alleged to have made contact with the eyes / eye area of Northampton Saints hooker Dylan Hartley during the first-half of the Round 4 reverse, a match that also saw No8 Xavier Rush sent off for the Blues.
Rees has been charged under Law 10.4(m) 'Contact with the eye / eye area; Acts contrary to good sportsmanship', with his case set to be heard by independent Judicial Officer Pat Barriscale from Ireland.
The IRB recommended sanction for the offence is as follows: Low End: 12 weeks; Mid Range: 18 weeks: Top End: 24+ weeks; Maximum: 156 weeks.
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