The competition's foul play review committee found the ruling after Williams was cited for his entry to a ruck early in the match at Hamilton on Saturday, with his shoulder deemed to have connected with the head of All Blacks team-mate Tupou Vaa'i.
The committee said the act of foul play merited a "mid-range entry point" punishment of six weeks but that was halved after the 25-year-old's remorse and his disciplinary record were taken into account.
"Williams was also given permission to apply to take part in World Rugby's Coaching Intervention Programme as a substitute for the final match of the sanction," the committee said in a statement.
The 27-test veteran will miss this weekend's match against the Blues at Eden Park, followed by games against the Highlanders in Christchurch and Moana Pasifika on the North Shore.
