Resources assigned to the operation to a particular department exceeds the resource assigned to that

Hello all,

I have assigned 3 units UOM each of machine resource to Machine department. But when I assign operations resources to a particular resource in the machine department, I can assign more than 3 units.

How can we assign more than the resources assigned to a department to the operations to that particular department.

Sample

Departent : Machine

Resource : Lathe        Qty : 3 UOM - each

standard Operations : turning

1. From department form assigned 3 lathes to resource

2. Assigned standard operation turining to department machine.

3. From operations resource form for turning in machine department, i can assign more than 3 lathes. TAB- Scheduling , Assign units : 4

I want to make sure that not more than 3 lathes are assigned to the operation turning in machine department.