The red card was issued for use of the head on Ospreys replacement scrum half Jason Spice.
Martyn Williams will be free to play rugby again on the Sunday 14th January 2007.
Williams handed three week ban
The ban was been issued following a meeting of the WRU Disciplinary Sub-Committee on Thursday 28th December 2006 which evaluated the incident which took place in the Cardiff Blues v Ospreys Magners League match at Cardiff Arms Park on Saturday 23rd December 2006.
