Two umpires have been banned by the International Tennis Federation and four more are being investigated over allegations of fixing.
The ITF has revealed it barred Kazakhstani Kirill Parfenov for life in February 2015 and suspended Croatia's Denis Pitner for a year last August.
Four others are being investigated for allegedly taking bribes to manipulate scores on the Futures Tour.
This follows BBC and BuzzFeed claims of match-fixing at tennis' top level.
That joint investigation uncovered files showing that, over the past 10 years, 16 high-ranking players have been repeatedly flagged to the Tennis Integrity Unit (TIU) over suspicions they have thrown matches.