Players have unlimited opportunity to challenge, however if three incorrect challenges are made in a set, they cannot challenge again until the next set. If the set goes to a tie break, players are given additional opportunities to challenge.
How the On-Court Player Challenge System Works
Each player is allowed a maximum of three incorrect challenges in a tiebreak set after which they are not permitted to challenge again in that set.
Challenges may not be carried over from one set to another.
In the Advantage set - 5th set for men's singles and 3rd set for women's singles
However, if the match is tied at six games all, the counter is reset with both players again having a limit of up to three incorrect challenges in the next 12 games
Challenges may not be carried over and the process of resetting is repeated after every 12 games
NOTE:
The Chair Umpire will decide to use the Electronic Review when there is doubt by a player about the accuracy of the line call or overrule. The Chair Umpire may refuse the Electronic Review if he/she believes that it is not made in a timely manner and can only be made on point-ending shots or when a player stops play. If the Official Video Review is unavailable for any reason, then the 'original' call will stand.