Referees have been told to be more vigilant over shoulder charges after two of the three players suspended for incidents in last weekend's round of matches escaped any on-field action.

Manly prop Willie Mason (two matches), Warriors forward Ben Matulino (three matches) and Canberra centre Joey Leilua (one match) doubled the number of players suspended for shoulder charges this season after the NRL last week amended the wording for the match review to lay a charge from requiring contact with the head or neck to one made with "force".

However, Mason and Matulino, who both attracted 50 per cent loading for previous shoulder charge offences, were not penalised for their respective hits on South Sydney's Thomas Burgess and St George Illawarra five-eighth Gareth Widdop.

"I have spoken to the referees and we have gone back through some positional play because clearly the person in the best position to see it is the referee who is behind the ruck because they can actually see the tucking of the arm," NRL referees boss Tony Archer said.