1. Competitors must follow the marked course in correct sequence from start to finish and must pass all control points.

2. If a competitor skis on a wrong section or leaves the marked course, (s)he should return to the point where the error was made. In order to do so, the competitor may have to ski against the correct ski direction and shall be totally responsible for ensuring that there is no obstruction and for ensuring the other competitors are not endangered.

3. Competitors must cover the whole distance on their skis using only their own means of propulsion. Help from outside pacemakers is not allowed.

4. In classical technique competitions, the competitors must use classical technique only.

5. In Interval Start competitions, any violation of classical technique (for example skating strides to maintain or increase the speed) will be considered to affect the results (due to improved time), and the jury will apply the appropriate sanction regardless of the time difference between skiers, even for a winning athlete.

6. Obstruction is not allowed in any competition. Obstruction is defined as deliberately impeding, blocking, charging or pushing any competitor with any part of the body or ski equipment.

7. Waxing, scraping or cleaning of the skis during competition is forbidden in freestyle technique competitions, but allowed in classical technique competitions, where the athletes may scrape their skis to remove snow and ice and add wax, if necessary. Competitors may only be handed tools or materials, but the athletes, themselves, must do everything else outside of the track without further assistance.

In order to preserve the integrity of a classical cross-country ski race, officials are spread across the race course looking for technique violations.

Violations commonly occur in the following situations: 

On the corners: If tracks exist on a corner, racers must stay within those tracks by using classical technique. If no track exists on a corner, racers are allowed to use a turning technique by pushing off the inside of one ski to complete the turn. Sections of the course where a turning technique is allowed are marked for the racers.

Switching tracks: Changing tracks in the middle of the race is legal. A cross-country racer will step from one set of tracks to another in attempt to improve their position. If a racer changes tracks repeatedly, especially on hills where the steps can give them more power to ski the incline, they will be assessed a violation. 

Herringbone technique: Stomping up hills with skis in a V-pattern, known as herringbone technique, is legal until the skis begin to slide out from under the racer. Once a ski begins to slip, a racer has a tendency to push off from the inside edges. This is considered skating or freestyle technique, and the racer will be assessed a violation. 

Disqualification: If a racer is assessed two violations in a single race, referred to as yellow cards, that skier will be disqualified from the event.