What is the referee's authority, and who can question a decision?

The referee is the sole judge on all match related matters inside the perimeter for the duration of the match, with jurisdiction over all players, coaches and officials. The referee is required to:

• inspect the field of play, line markings and markers before the match to ensure safety;
• adjudicate on the rules of the game;
• impose any sanction necessary to control the match;
• award tries and record the progressive score;
• maintain a count of touches during each possession;
• award penalties for infringements; and
• report any sin bins, dismissals or injuries to the relevant competition administration.

Only team captains may seek clarification of a decision directly from the referee, and only during a break in play or at the referee's discretion. Team coaches and officials at the end of the field must stay at least five metres from the dead ball line and must not coach or communicate with the teams or referees. Disputing decisions is listed as misconduct.

Source: FIT Playing Rules 5th Edition, rules 6, 20.1.3 and 25.