The NBA will begin experimenting with coach's challenges in the 2019 Summer League, a system which has already been tested out in the G League over the last two seasons.
According to ESPN's Zach Lowe, a league memo regarding the coach's challenges states:
"Coaches will get one challenge per game, and they will lose it even if the challenge is successful, according to the memo. They can use it to challenge only called fouls, goaltending, basket interference, and plays when the ball is knocked out of bounds, the memo says."
In order to challenge a play, coaches must have a timeout remaining, and the team must call a timeout immediately after the incident they wish to challenge takes place.
According to the memo sent to ESPN, the coach must "twirl his/her index finger toward the referees" aka the universal sign for "review that!" to signal for the challenge. If the challenge is successful, the team will not lose the timeout but if the call on the court stands they will lose the timeout.
The league reportedly anticipates using the challenge rule in the 2019-20 regular season as part of a pilot program. In order for the rule to be implemented for the upcoming season, two-thirds of the league's teams will need to approve of it in a formal vote of the board of governors. That vote will reportedly take place on July 9.
According to the memo, "Based on the feedback we have received, we expect it to be adopted."