According to NFL Network's Ian Rapoport, Williams violated the league's substance-abuse policy.
The Cowboys placed the 29-year-old on injured reserve earlier this month. Williams isn't eligible to return until Dallas' Week 14 matchup with the Philadelphia Eagles on Dec. 9, so his suspension ultimately won't result in him missing any more playing time.
The punishment stems from Williams' arrest in May on a charge of misdemeanor public intoxication. Frisco, Texas, police had discovered Williams' 2017 Lamborghini crashed into a light pole with no driver at the scene. They later found him riding an electric bicycle near his home.
Authorities dropped the charge in August after Williams completed an alcohol awareness class and paid $2,680.11 for the damages to the light pole.
Williams has appeared in three games this season, catching two passes for 18 yards. Prior to going on injured reserve, he missed Dallas' 26-24 win over the Detroit Lions in Week 4.
The Star-Telegram's Clarence E. Hill Jr. reported in October that Williams had missed practice prior to that game "as he continues to work through a range of [off] the field issues with the team's approval."