A source said the penalty falls under the NFL's substance abuse policy stemming from a summer intoxication arrest.
The Cowboys placed Williams on injured reserve Oct. 6, in part because of a foot injury that required surgery during the offseason.
The league said Thursday the suspension will be in effect Sunday when the Cowboys visit Washington. After Dallas' open week and a home game against Tennessee, the final game of the ban will be Nov. 11 at Philadelphia.
But Williams will miss at least three more games after that while on injured reserve. His first possible game is Dec. 9 at home against the Eagles.
In August, Williams' misdemeanor public intoxication charge was dismissed after he attended an alcohol-awareness course and paid the city of Frisco for property damage caused when his Lamborghini knocked over a light pole in May.
During training camp, Cowboys executive vice president Stephen Jones said he did not believe Williams would be punished by the league, although a player does not need to be found guilty in the legal system to face NFL discipline.
Williams is in the second year of a four-year, $17 million deal he signed in 2017. He had two catches for 18 yards in the first three games this season and played only 39 snaps. He is eligible to return to action off injured reserve on Dec. 9 at Philadelphia. He can serve his suspension while on injured reserve.
Because he was punished under the substance abuse policy, he can still remain around the team while serving the suspension.