The announcement was made a few minutes before 5 p.m. ET, and about 40 minutes before the scheduled first pitch.
Fifteen minutes after the announcement, the grounds crew at Wrigley Field rolled the tarp out onto the diamond.
Another update on the status of the game is expected to come at 6 p.m. ET.
According to Accuweather, there is a 50 to 70 percent chance of rain throughout Tuesday afternoon and evening in Chicago.
With the Cubs holding a 2-1 series lead, both clubs have discussed contingency plans in the event Game 4 is postponed until Wednesday.
Cubs manager Joe Maddon said scheduled Game 4 starter Jake Arrieta would still be on the mound if the game is pushed to Wednesday.
Nationals skipper Dusty Baker said he’s not sure whether his team would go with Tanner Roark or Stephen Strasburg if the game is pushed back. Roark is scheduled to start on Tuesday. Strasburg, who started Game 1, would be on normal four days’ rest if Game 4 is played Wednesday.