The International Tennis Federation (ITF) secretly banned two umpires last year, while four others are being investigated over allegations of corruption. The revelations add to the growing scandal in the sport.
Kirill Parfenov, an umpire from Kazakhstan, was banned for life by the ITF in February 2015, and Croatia's Denis Pitner received a one-year suspension last August.
The Tennis Integrity Unit (TIU) is also investigating four other umpires for allegedly taking bribes from betting syndicates to manipulate scores on the Futures Tour - a third-tier men’s tour which sits below the ATP and Challenger tours.
Parfenov's life ban was for contacting another official on Facebook to try and manipulate the scoring of matches, while Pitner was suspended after it was found he had sent information about a player to a coach during a tournament, and also frequently logged on to an account from which bets were placed on tennis matches.
This is the latest scandal to hit tennis, following the recent claims made by the BBC and BuzzFeed of match-fixing at the highest level in the sport.
The report said 16 players who have been ranked in the top 50 had been repeatedly brought to the attention of the TIU over concerns they had thrown matches.
The latest investigation, carried out by the Guardian newspaper, claims umpires on the Futures Tour have been 'courtsiding' - a practice which allows gamblers to place bets before bookmakers have up-to-date information.
Umpires on the Futures Tour update the scoreboard themselves after each point before the information is submitted to bookmakers and live-score sites.
By delaying the scores by up to a minute, gamblers are then able to place bets already knowing what the outcome would be.
Richard Ings, a former professional umpire, says the revelations are “deeply troubling.”
“Over a 15-year period I have been involved in professional tennis officiating both as a professional umpire and administrator of officiating for the ATP,” he said. ”During that period I have seen tennis umpires breach the code for officials for relatively minor offences. But I have never before seen umpires breach it for tennis-integrity issues related to gambling on tennis and courtsiding.
“It is deeply troubling, but not at all surprising, that the risk to the integrity of tennis driven by gambling has expanded beyond players and their entourages to now include umpires and other tournament officials.”
Data company Sportradar facilitates the system which supplies data to 'in-play' betting sites across the globe.
The ITF says the contract with Sportradar provides regulation and control previously not available to the sport.
“Our agreement with Sportradar, like those in place with ATP and WTA, by creating official, accurate and immediate data, acts as a deterrent to efforts by anyone trying to conduct illegal sports betting and/or unauthorized use of data for non-legal purposes,” an ITF statement said.
“Sportradar are excellent partners and share with the ITF the goal of ensuring the integrity of our sport.”
When asked why the latest suspensions had only just been revealed, the ITF confirmed its Code of Conduct for Officials had not required those sanctioned to be named, until the code was amended at the start of 2016.