Wales flanker Williams has been cited for allegedly dropping his knee into the face of Edinburgh full back Chris Paterson during Cardiff Blues' 18-17 win in the Welsh capital on Saturday night.
The veteran openside has been cited under Law 10.4(a) 'A player must not strike an opponent with the knee(s)' and faces between a three and 52-week ban if found guilty.
A three-week suspension would leave Williams unavailable for Friday's Heineken Cup trip to Castres, as well as the Magners League Welsh derby with the Scarlets and the Round 7 fixture at Aironi.
New Munster signing Tuitupou is alleged to have committed a dangerous tackle on London Irish scrum-half Paul Hodgson during the first-half of the 23-17 loss in Reading.
The former Worcester Warrior has been charged with 'Lifting a player from the ground and dropping or driving a player into the ground' and faces a similar possible punishment to Williams.
The low end sanction recommended by the International Rugby Board is three weeks; the mid range punishment is six weeks; the top end is 10 weeks plus; and the maximum sanction is a full year.
If found guilty at any level, Tuitupou will miss Munster's European clash at home to Toulon and the Magners League fixtures with Benetton Treviso and Ulster.
Fa'amatuainu has been cited for allegedly committing a dangerous tackle on Perpignan wing Adrien Plante during the second half of the Scarlets' stunning bonus-point win in Llanelli.
The minimum sanction for such an offence is two weeks; the mid-range is six; the top end is 10 weeks plus; and a tackle of the maximum severity carries a 52 week ban.
A three-week suspension would prevent the Samoan forward from featuring against Leicester Tigers at Welford Road and stop him from playing any part in the Magners League clashes with the Blues and Glasgow Warriors.
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