Physical activity and exercise are advised for back pain, but this usually refers to chronic back pain (lasting three months or more). In acute back pain following an accident or injury, rest and light activity are more appropriate.
Most ski instructors lift, carry, reach, bend, and push/pull equipment and people during work hours. In the acute phase of a back injury, any of these activities can lead to further injury. In addition, it's common for some ski instructors to spend long periods of time standing. This type of inactivity can cause muscle spasm and increased symptoms.
You might want to take a day or two off if you have sick leave available. Rest and recover before hitting the slopes again. If possible ask for a reduced workload when you first come back. This may help ease you safely back into a full-day schedule. Take some time to get warmed up before jumping into your regular activities.