In a strongly-worded letter to Bill Beaumont, the World Rugby Chairman, the group, which includes former Scotland centre Sir Ian McGeechan, branded the sport "unnecessarily dangerous" and said action must be taken.
Referencing comments made by former Wales and Lions captain Sam Warburton that unless something is done a player could die on live television, the letter pleaded: “So, no more empty words, we call upon Sir Bill to act now in the profound hope that Sam Warburton’s words do not become prophetic.”
One change called for by the group, which also includes Sir Gareth Edwards, Willie John McBride, Barry John and John Taylor, is a reduction in the number substitutes permitted by each side from eight to four to limit the number of dangerous collisions that take place in the latter stages of games.
The letter reads:
"In our opinion, professional rugby union has become unnecessarily dangerous.
"For fear of losing their livelihood, current players dare not speak out, but those liberated by recent retirement clearly agree. Dylan Hartley, the former England captain, described his generation as 'crash dummies'. His Wales and Lions counterpart Sam Warburton, fears that 'if something is not done soon, a professional player will die during a game in front of TV cameras'.
"It would be grossly negligent to allow the status quo to continue.
"Fifty years ago four of our signatories were part of a Lions team that clinched their only ever series victory over New Zealand and three years later three of them were members of the first Lions to defeat South Africa in the modern era.
"We all admire today’s players who are fitter, bigger and stronger than we were, but the risks they are expected to take are, in our opinion, unacceptably high.
"Rugby Union was conceived as a 15-a-side game for 30 players. With the current eight substitutes per side, many of whom are tactical ‘impact players’ or ‘finishers’, this can and often does stretch to 46.
"More than half a team can be changed and some players are not expected to last 80 minutes so train accordingly, prioritizing power over aerobic capacity. This shapes the entire game leading to more collisions and in the latter stages numerous fresh ‘giants’ crashing into tiring opponents.
"The simple change we advocate is to allow eight subs on the bench if you must but limit the number that can be used to four and then only in the case of injury. This will make the game safer, a view supported by leading players and eminent members of the medical profession.
"We know that World Rugby Chairman Sir Bill Beaumont agrees with us. In January 2020, he expressed his concern that “rugby had become a game for big people” and backed a trial law whereby players could only be replaced if injured.
"Sadly, more than 18 months later World Rugby has done nothing – yet again it stands accused of all words and no action.
"So, no more empty words, we call upon Sir Bill to act now in the profound hope that Sam Warburton’s words do not become prophetic."