There comes a time when a Daily Organiser has to decide whether to run a very small class or not. An example is elective classes (say combined Year 9/10’s), where the year 9’s may be on a camp, leaving only 1 or 2 year 10’s in the elective.
If the day requires a lot of covers, and covering teaching staff are limited, you may have to join up the class with another smaller one.
Remember, it is not the Daily Organisers job to keep every teacher happy about arrangements. Your job is to help run a school and ensure that legal responsibilities of supervision of students is maintained. Sometimes teachers may not see the big picture going on the school. You can only be as fair as you can be and do the best with the available resources you have at hand. Explain the situation courteously with any disgruntled staff then move on. There are more important things that you have to worry about.