First, here are some definitions :
Call duty in an establishment (art. 12.09) Corresponds to clinical work performed in the evening from Monday to Friday, after the regular work day, and during the day on weekends.
Night call duty in an establishment (art. 12.10) It is performed from 20:00 onward, on weekdays and on weekends.
Then, here are some provisions of the collective agreement :
Limit of the number of calls You may perform up to 6 calls in an establishment and up to 20-night calls during a 28-day period. Limit of the number of weekends worked You must have two weekends off for each 28-day period.
Alternate limit between night calls and any work schedule It is forbidden to alternate more than once per 7-day period between night calls and any other work schedule.
These last three provisions limit the total number of call duties (see articles 12.09 to 12.11).
Thus, you will never be able to reach both call duty limits (6 calls in an establishment and up to 20-night calls) during a 28-day period.
It is still possible to perform a total of more than 6 calls in a 28-day period, since you can be asked to perform both types of call in the same 28-day period. However, the provisions mentioned above must always be respected.