A report published on Tuesday found that racism exists at every level of elite rugby, including the England team.
The report was commissioned by the Rugby Football Union (RFU) after former England centre Luther Burrell reported racist abuse he received during his career.
"The qualitative research found that in every area of elite rugby -- men's and women's, national team, clubs and academies -- players had experienced some form of racism," the report, called Purpose Union, said in its key findings.
In an interview with the Mail on Sunday last year, Burrell, who won 15 caps for England and played for Leeds, Sale, Northampton Saints and Newcastle, said racism was rife in the sport, detailing comments that were discriminatory but were passed off as "banter."
Burrell, 35, also highlighted the use of a racial term in a WhatsApp group chat.
After the publication of the interview, Newcastle launched an investigation to determine whether any of the incidents occurred during Burrell's time at the club, before asking the RFU to conduct the investigation.
The RFU said it had interviewed 93 Newcastle employees as part of the inquiry.
"On balance of probability, the allegations made in the Mail on Sunday article are true but there is insufficient evidence to say whether all the allegations occurred at the club, apart from the WhatsApp message which contained a racist comment," the RFU said in a statement.
"The player was found to be subject to a further two specific incidents of racial abuse... there was support for the allegations in the evidence of at least two other employees of the club.
"The player's evidence was found to be reliable and his motivation for making the allegations was his wish to eradicate racist behaviour from rugby union."
Burrell said the RFU's findings have given him a "sense of closure."
"To call anybody a slave is not funny, so it was abhorrent behaviour," Burrell told the BBC. "I have children and friends with children who love rugby, and I cannot be having them exposed to these micro-aggressions and perceived banter.
"This has not been a witch hunt. It's not about retribution. This is about me finally having my voice heard. I've always said that this has ultimately not been about me, this has been about generational change within the sport."
The RFU said Newcastle had co-operated throughout the process, adding that the club would implement changes to policies and procedures including education, training and the establishment of clear whistle-blowing processes.
"Luther was very brave to come forward and share his experiences of racism and classism in the game and he has the continued support of the Union," RFU chief executive Bill Sweeney said.
In a separate statement, the RFU announced an Inclusion and Diversity Action Plan for the elite game, saying Burrell's revelations had "necessitated a deeper look at these issues and the broader culture within the elite end of the game".
The RFU said that it, along with Premiership Rugby (PRL) and the Rugby Players Association (RPA), had commissioned independent research into experiences of class discrimination and racism in the elite game between September and December.
The governing body said the recommendations of the research were used to "listen to the experiences of those in all elite rugby clubs and to agree an action plan."
Measures and goals proposed in the plan include game-wide inclusion and diversity education, active bystander training for clubs and academies as well as the development of greater access to higher levels of the game for under-represented groups.