The Sydney Roosters have been issued with a $5,000 breach notice over comments coach Brian Smith allegedly made to referees at halftime in the NRL club's win over Canberra on Sunday.

The league says Smith directed comments on the penalty count to whistleblowers Ben Cummins and Tony De Las Heras during the break in the Canberra Stadium match, won 22-12 by the Roosters.

"Reports from the referees and the ground manager confirmed the comments were directed against the officials as they walked towards their change room and related to the penalty count in the match," the NRL said in a statement.

The league said clubs had been warned in May after a number of incidents where club officials had gone close to breaching the rules relating to match officials.

"We can't have a situation where coaches or club officials make comments to referees on game day, particularly when the match is still in progress," NRL chief operating officer Graham Annesley said.

"There are plenty of opportunities for clubs to voice their disagreement with refereeing decisions but the time to pursue these is not when emotions take over at a match."

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