The NRL has issued St George Illawarra with a breach notice proposing a fine of $10,000 over comments by its coach Paul McGregor last weekend.

The breach notice was issued following McGregor's post-match statements that decisions made by match officials were "embarrassing" and "incompetent".

"In simple terms, the rule is that coaches, players and officials should not discuss referees and their performances in the public domain," NRL Head of Football Brian Canavan said.

"We have been pragmatic in dealing with instances where comments have been made but the competence and integrity of referees has not been questioned.

"But it is our view that these particular comments crossed the line.

"All coaches should be aware that they risk sanctions if they discuss the performance of referees."

The Dragons have five business days to respond to the breach notice.