Requirement to make TECO mandatory before CLSD in Maintenance Order

Team,

I have a requirement for Maintenance Order

At present, User can CLSD the Order, without doing TECO, by bypassing the User Status sometimes. Since I cannot make any changes to user status..Now, I have a requirement, that : If a Maintenance Order is not TECO, and if user tries to CLSD the Order, system should give me an error message : Maintenance Order is not TECO.

I want to implement this logic, and I want to know, in which exit, i can write this.

Can anyone help me in this. Please treat this as an urgent.