Referees have been told to adopt a zero tolerance policy towards reckless play following a series of high-profile incidents in recent years.
The most serious was the death of Neath scrum-half Gareth Jones last season. The Cardiff player subsequently cited was cleared by the Welsh Rugby Union.
Now the International Rugby Board (IRB) wants to rid the game of the clearing-out practice at rucks.
The IRB has issued a memo to all member unions ordering the tough stance.
It will be introduced at this weekend's start to the new season.
Neath captain Lee Beach welcomed the new law.
"The rule that you can't come in and shoulder challenge is good," he said. "I used to do it in the past.
"Now either players will get sent off or penalised for it and hopefully the referees will take that on board."
The IRB made the decision after taking advice from the medical and legal professions.
"There is a growing concern...about the conduct of players when entering rucks and mauls...which is considered dangerous," David Carrigy of the IRB said in the memo.
Officials are being instructed to adopt zero tolerance to any player charging into a ruck or maul who is not bound to a team-mate as the laws require.
This is a change in interpretation that could prove as significant as the new experimental law variations.
They will also clamp down on players who clear out opponents not involved in a ruck or maul.
IRB referees' manager Paddy O'Brien said: "The law is there to protect players and we felt referees weren't applying the law as strictly or stringently as we should be.
"Every game you watch at any level, there are players who are entering breakdowns with no respect for the body of the player they are going to clean out as some call it.
"It is not cleaning out, it is foul play."
Wales captain Ryan Jones was injured in the Six Nations match against Ireland last season following reckless play by Bernard Jackman.
And in the Tri Nations, Australia's Stirling Mortlock was injured by a challenge from South Africa's Bakkies Botha.
Pontypridd captain Nathan Strong said the rule was "good for the game," but added: "These are one-off incidents and rugby is a physical game.
"I enjoyed flying into rucks trying to clean out the competition.
"If the ball is on the floor, the competition is there for it."
The Welsh Rugby Union cleared Cardiff centre Darren Ryan of reckless play after he was cited over the incident involving Gareth Jones in May.