Order type not to create manually but only using maintenance plan

Hi,

My client has one requirement.

They have a maintenance order type ZM01. This order type is assigned in the maintenance plans.

Till now they were created when maintenance plan was getting scheduled and also created manually using IW31.

Now the requirement is " User's should not be able to create ZM01 order manually using IW31 but it should only get created when the maintenance plan is scheduled". The users should be able to change and display them. How can this be achieved?

Regards,

Smart