THE NRL yesterday moved to clear-up the contentious shoulder debate amid round two confusion where Melbourne's Billy Slater was charged by the match review committee but South Sydney's Nathan Merritt avoided any suspension.

Storm skipper Cam Smith came forward yesterday to question the perceived inconsistency before the NRL explained exactly why only one of the players was charged.

Slater was eventually charged with dangerous contact but will play Canterbury tomorrow night at AAMI Park through an early plea.

Merritt was penalised for a hit on Cronulla's Matt Wright on Sunday night. Slater was charged after he struck Cowboys' Antonio Winterstein.

"I am not sure what's gone on, if the rules have changed, if the referees interpret it differently now. But it's inconsistent," Smith said.

"Bill made a similar effort to tackle as Nathan Merritt and there are two different outcomes. That's the frustrating thing for players and coaches, those inconsistent rulings. At the moment it seems to change every week.

Not happy Cam: Smith fuming over Slater charge

"I didn't see Bill's incident until (Monday night) and he brushed over his head and got him high and we all know if you get someone high you are going to be in strife.

"But for me, and I actually spoke to the referees during the game on Saturday night, we were told at the start of the year that any tackle made where there was no wrapping motion of the arms, just using your shoulder to bump someone, was going to be penalised.

"I have seen something in every game played this year and it has just been let go until someone is hit high or if it looks spectacular and they've been knocked off their feet."

Responding to Smith, NRL general manager of football operations Nathan McGuirk claimed the rules were "clear" and set in concrete.

"The rules around shoulder charges are quite clear," McGuirk said.

"When a player commits a shoulder charge which makes contact with the opponent's shoulder or chest this will be dealt with by the match officials on-field through a penalty.

"If a player commits a shoulder charge which makes contact with the head or neck of an opponent, not only will he be penalised but also face further action by the referee and possibly by the match review committee.

"In the case of Nathan Merritt's tackle, the match review committee deemed that no contact was made to the opponent's head or neck, therefore a penalty was deemed sufficient."

Smith said Storm officials were likely to seek further clarification on the rule ahead of the club's grand final re-match with Canterbury.

"I'm sure after Bill getting cited they'll be contacting some people to find out what's going on," he said.